The Trail Running Glossary: Every Term Explained, FKT to Vert

The complete trail running glossary: vert, D+, FKT, DNF, ITRA points, cutoffs, mandatory kit and every training term you will meet, in plain language.

Every sport has its jargon, and this trail running glossary exists because ours is unusually impenetrable. A single race report can contain FKT, D+, vert, DNF, ITRA points, a Running Stone, and a cutoff, and none of it is explained because everyone assumes you already know. This is the reference: every term you will meet in race documents, on forums, and in training plans, defined properly and grouped so you can find what you need. Bookmark it and stop nodding along in conversations.

Trail running glossary: distance, terrain and elevation

Vert. Short for vertical gain, the total metres or feet climbed on a route. Trail runners often describe a run by its vert rather than its distance, since 20 km with 1,500 m of vert is a completely different day from 20 km flat.

D+ and D-. European notation for positive elevation gain and negative elevation loss, in metres. A race listed as 42 km, 2,700 m D+ has 2,700 metres of climbing.

Gradient. The steepness of a slope, expressed as a percentage. A 10% gradient rises 10 m over 100 m of horizontal distance. Above roughly 15 to 20%, most runners switch to hiking.

Technical. Terrain with roots, rocks, loose scree, or anything requiring you to watch your feet. The opposite of buffed or flowy.

Singletrack. A trail wide enough for one runner. Doubletrack fits two abreast, and fire road is a vehicle-width track.

Runnable. Terrain gentle and smooth enough to run continuously. A race described as runnable usually means a faster field and less hiking.

Switchback. A hairpin turn used to make a steep slope climbable. Cutting them causes erosion and is the most common etiquette failure on trails.

Scree and talus. Loose rock. Scree is small and slides underfoot, talus is larger and requires stepping between blocks.

Exposure. Terrain where a fall would have serious consequences, typically a ridge or a traverse with steep ground below.

Col, pass, saddle. The low point on a ridge between two peaks, and usually the point a trail crosses it.

Out and back, loop, point to point. Route shapes. Point to point races need transport logistics between start and finish.

Race formats and distances

Ultramarathon. Any race longer than a marathon, so 42.2 km. In practice the common distances are 50 km, 50 miles, 100 km, and 100 miles.

Skyrace. Mountain races typically between 20 and 45 km with very high vertical relative to distance, often above 2,000 m of climbing, run at high intensity. Zegama-Aizkorri, covered in our race guide, is a well-known example.

Vertical kilometre, or VK. A race climbing 1,000 m in under 5 km of distance. Brutally steep and usually hiked.

Stage race. A multi-day event with a separate timed stage each day and cumulative results.

Backyard ultra. A last-runner-standing format where competitors run a 6.7 km loop every hour until only one remains.

FKT. Fastest Known Time, an unofficial speed record on an established route rather than in an organised race. Categories are unsupported, self-supported, and supported.

DNF. Did Not Finish, whether by withdrawal or by missing a cutoff. Our DNF guide covers how to handle one.

DNS. Did Not Start.

Cutoff. A deadline for reaching a checkpoint. Missing one ends your race. Our cutoff times guide explains how they are set.

Mandatory kit. Equipment a race requires you to carry, typically a waterproof jacket, warm layer, headlamp, cup, phone, and survival blanket. Checked by spot inspection, with disqualification as the penalty.

Rankings, qualification and points

ITRA points and ITRA Performance Index. The International Trail Running Association rates races by difficulty and assigns runners a performance index from their results (International Trail Running Association, 2026). Many races use the index for seeding or qualification.

UTMB Index. UTMB's own performance rating, calculated by distance category: 20K, 50K, 100K, and 100M. It gates which UTMB World Series races you may enter.

Running Stones. Lottery tickets in the UTMB entry system, earned by finishing World Series events. Our UTMB lottery guide covers the mechanics.

Golden Ticket. A direct entry to Western States awarded to top finishers at selected qualifying races.

Qualifier. A race you must complete, usually within a time standard, to become eligible to enter another race or its lottery.

Training terms

Base. A phase of mostly easy aerobic running that builds the foundation intensity work is layered onto.

Threshold. The intensity at which lactate begins accumulating faster than you clear it, roughly the hardest effort you could sustain for an hour.

VO2 max. The maximum rate at which your body can use oxygen. Our VO2 max versus lactate threshold guide covers which matters more in the mountains.

Polarized training. An intensity distribution where most sessions are genuinely easy and a small proportion are genuinely hard, with little time spent in the middle (Seiler & Kjerland, 2006).

Periodization. Structuring training into phases with different goals across a season.

Taper. The reduction in training volume before a race, typically over one to three weeks.

Power hiking. Deliberate, efficient uphill walking, often with poles. Above roughly 15 to 20% gradient it is more economical than running (Minetti et al., 2002).

Vertical pace, or VAM. Vertical metres climbed per hour. A useful measure of climbing fitness, with 600 to 1,000 m/hr typical for trained trail runners on sustained climbs.

Back to back. Consecutive long runs on Saturday and Sunday, used to build fatigue resistance for ultras.

Time on feet. Training measured by duration rather than distance, which suits trail running where pace varies enormously with terrain.

Fatigue resistance, or durability. The ability to hold pace and economy late in a long effort, increasingly recognised as a better predictor of ultra performance than VO2 max.

Fueling and hydration

Bonk, or hitting the wall. Running out of available carbohydrate, producing a sudden collapse in pace and mood.

Gut training. Progressively increasing carbohydrate intake during training runs to raise how much you can absorb without GI distress.

Multiple transportable carbohydrates. Combining glucose and fructose to exceed the roughly 60 g per hour ceiling that glucose alone imposes.

Hyponatremia. Dangerously low blood sodium, usually caused by drinking too much rather than too little.

Sweat rate. How much fluid you lose per hour, measurable with a scale. Our sweat rate testing guide covers the protocol.

Soft flask. A collapsible bottle that shrinks as you drink, reducing sloshing.

Race day and logistics

Aid station. A supported checkpoint with water, food, and often medical support.

Drop bag. A bag you pack in advance and the organisers transport to a specified aid station.

Crew. People who meet you at permitted access points with kit and food. Our crewing guide covers the job.

Pacer. Someone who runs with you for part of a race, usually permitted only in the later stages.

Sweeper. A volunteer running at the back to ensure nobody is left behind, often enforcing cutoffs.

Buckle. The finisher's award at many 100 mile races, particularly in North America.

Death march. The final hours of an ultra spent walking, when running has stopped being possible.

Chafe, and hot spot. Skin friction damage, and the tender patch that precedes a blister.

Bonus miles. Extra distance run by getting lost.

Key takeaways

  • Vert and D+ describe climbing, and matter more than distance in trail running
  • Technical describes terrain requiring foot placement, not difficulty in general
  • ITRA and UTMB indices are separate systems that both gate race entry
  • Cutoffs are intermediate deadlines, not just a finish time limit
  • Time on feet is the more useful training metric on terrain where pace varies wildly

Where to go from here

Use this glossary as a jumping-off point rather than a reading exercise. Most of these terms link to a full guide, and the ones that matter most for a first ultra are cutoffs, mandatory kit, drop bags, and vert.

When you are ready to turn the vocabulary into a plan, Trailia builds elevation-aware training around your goal race, using the terms above as actual variables rather than jargon.

Citations

  • Minetti, A. E., Moia, C., Roi, G. S., Susta, D., & Ferretti, G. (2002). Energy cost of walking and running at extreme uphill and downhill slopes. Journal of Applied Physiology, 93(3), 1039-1046.
  • International Trail Running Association (2026). ITRA Performance Index and race categorisation documentation.
  • UTMB World (2026). UTMB Index and Running Stones documentation.
  • Seiler, S., & Kjerland, G. O. (2006). Quantifying training intensity distribution in elite endurance athletes: is there evidence for an optimal distribution? Scandinavian Journal of Medicine & Science in Sports, 16(1), 49-56.

Frequently Asked Questions

What does vert mean in trail running?

Vert is short for vertical gain, the total height climbed on a route, measured in metres or feet. Trail runners often describe a run by its vert rather than its distance, because 20 km with 1,500 metres of climbing is a completely different day from 20 km flat. In European race listings it appears as D+.

What does D+ mean on a race profile?

D+ is European notation for positive elevation gain in metres, while D- is elevation loss. A race listed as 42 km with 2,700 m D+ climbs 2,700 metres in total. The two numbers together tell you far more about a course than the distance does.

What is an FKT?

Fastest Known Time, an unofficial speed record on an established route rather than in an organised race. Attempts are categorised as unsupported, meaning you carry everything, self-supported, meaning you can resupply, or supported, meaning you have a crew. Records are submitted to community-run registries with GPS evidence.

What does DNF mean and how is it different from DNS?

DNF means Did Not Finish, covering both voluntary withdrawal and being pulled at a cutoff. DNS means Did Not Start, so the runner never began the race. Both appear in official results and count as non-finishes for qualifying purposes at most races.

What are ITRA points and the UTMB Index?

They are separate systems that both rate races and runners. ITRA, the International Trail Running Association, rates races by difficulty and assigns runners a performance index from results. UTMB runs its own index by distance category, which gates which of its World Series races you can enter.

What is technical terrain in trail running?

Ground with roots, rocks, loose scree, or anything that requires you to watch your foot placement rather than run freely. It describes the surface rather than overall difficulty, so a technical trail can be flat. The opposite is often called buffed, smooth, or flowy.

What is power hiking?

Deliberate, efficient uphill walking, frequently using poles and often with hands on the thighs for leverage. Above roughly 15 to 20% gradient it becomes more economical than running for most people. It is a trained skill rather than a fallback, and strong ultra runners practise it deliberately.

What is a vertical kilometre race?

A race that climbs 1,000 metres of vertical gain in under 5 km of horizontal distance. The gradients are steep enough that almost everyone hikes rather than runs. Winning times are typically between 30 and 45 minutes depending on the course.

What is a drop bag?

A bag you pack in advance that race organisers transport to a specified aid station, containing spare kit, food, socks, or lighting. It is the main way to access supplies at races where crew access is limited or prohibited. Label it clearly and pack it assuming you will be exhausted when you open it.

What does bonking mean?

Running out of available carbohydrate, which produces a sudden and dramatic collapse in pace, mood, and cognitive function. It is also called hitting the wall. The fix is consistent fuelling from early in the race, because once it happens recovery mid-effort is slow and incomplete.