Trail terms

Fastpacking

What is fastpacking?

Fastpacking is covering a multi-day route with a pack light enough to run in, somewhere between trail running and ultralight backpacking. Typical loads run 8 to 20 liters, and the trip is usually run downhill and on the flat and hiked uphill.

Pack size: About 8 to 20 L
Harness: Vest-style, not a hipbelt
Pattern: Hike up, run down and flat

What fastpacking is

Take an ultralight backpacking kit, cut it further until the pack is small and stable enough to run with, and cover the route at a mix of running and hiking. That's fastpacking. Packs are usually 8 to 20 liters with a vest-style harness rather than a hipbelt, because the load is light enough that your shoulders and chest can carry it and stability matters more than transfer.

How much of it you actually run

The pace is not what people assume. Almost nobody runs the whole thing. The usual pattern is power hiking the climbs, running the descents and the flats, and covering considerably more ground in a day than you would with a full pack, which is what lets a route that would be a five-day backpacking trip become a long weekend.

What it demands of your kit

What it demands is a genuinely honest kit list. There's no room for a comfortable camp, and margins are thinner in every direction: less insulation, less shelter, less food. That's fine on a summer route with escape options and a poor idea in the mountains in bad weather. The skill isn't running, it's knowing which trips suit the approach.

What this means when you're choosing

A pack that is stable when run in rather than merely small
A kit list honest enough to survive a night out if the plan breaks
Front-carry storage, since you cannot reach behind you at pace

The common mistake

Assuming you will run most of it

Almost nobody does. The usual pattern is power hiking the climbs, running the flats and descents, and covering ground through consistency rather than speed. Planning a route on your road running pace is how people end up finishing in the dark.

Common questions

How is fastpacking different from backpacking?

Mainly pack size and pace. A fastpacking kit fits in 8 to 20 liters and is carried in a running vest harness, which lets you run the flats and descents rather than walking everything.

Do you have to be able to run to fastpack?

Not really, and most fastpackers hike the climbs anyway. What matters more is a light kit and the fitness to keep moving for hours, which is a hiking skill as much as a running one.

Where this comes up

Guides on Tom's Hiking where fastpacking changes which product is right for you.

Going deeper

More in trail terms

Base weight

Base weight is everything in your pack except food, water and fuel: the gear that doesn't get used up. It's the number backpackers compare, because consumables vary with trip length while base weight is a property of your kit.

Ultralight

Ultralight is a style of backpacking built around a base weight under 10 lb. It gets there by making the big three lighter and by carrying fewer things, which trades comfort in camp and margin in bad conditions for comfort while walking.

Thru-hiking

Thru-hiking is walking a long trail end to end in one continuous trip, usually within a single season. The Appalachian Trail, Pacific Crest Trail and Continental Divide Trail are the best-known examples in the US, each taking several months.

Shoulder season

The shoulder seasons are spring and autumn, the months either side of settled summer conditions. Days can be warm and nights near freezing, weather changes faster, and gear that works in July is often not enough in late September.

Three-season

Three-season gear is built for spring, summer and autumn but not sustained winter conditions. It's the default rating for most backpacking equipment, and in practice it means handling rain, wind and light frost but not deep snow.

Layering system

A layering system is the practice of combining a moisture-moving base layer, an insulating mid layer and a protective shell, so you can regulate temperature by adding and removing pieces rather than relying on one heavy garment.

Zero day

A zero day is a day on a long trail where you walk no trail miles at all, usually taken in a town to rest, resupply and deal with logistics. A nero is a near-zero: a handful of miles into or out of town with the rest of the day off.

Nero day

A nero day, short for nearly zero, is a day on a long trail when you hike only a few miles and spend the rest of it resting or doing town chores. It sits between a full hiking day and a zero day, when you hike no miles at all.

Cowboy camping

Cowboy camping is sleeping outside with no shelter over you: a pad, a bag or quilt, and the sky. It saves the weight and the time of pitching a tent, and it trades away protection from rain, wind, dew, insects and anything that walks past in the night.

Postholing

Postholing is breaking through soft snow with each step and sinking to your shin, knee or thigh, leaving a line of holes behind you. It is exhausting, it can drop your pace to under a mile an hour, and it damages the trail for everyone following.

Slickrock

Slickrock is bare, exposed sandstone with no soil on it and no tread cut into it. You walk on the rock itself and follow cairns rather than a path. Dry sandstone gives excellent grip; wet or dusty sandstone gives very little, which is where the name misleads people.

Trailhead

A trailhead is the designated access point where a trail begins, and usually where you park and start walking. Many have a map board, signs or a toilet. The US Forest Service draws a firm line: a plain junction of two trails, or of a trail and a road, is not a trailhead.

Treeline

Treeline is the elevation, or latitude, above which trees can no longer grow. It is less a line than a zone where trees shrink into stunted, wind-shaped growth, and it sits at very different heights: between 5,000 and 6,000 feet in Washington's Olympics, and above 10,000 in the Sierra.

Backcountry

Backcountry is undeveloped land away from roads and drive-in campgrounds, reached on foot or by water. In US parks it is the opposite of frontcountry, where you drive to a campground, and camping there often needs a permit. It is not the same as legally designated Wilderness.

Big three

The big three are a backpacker's shelter, sleep system and pack: the three items where most of a kit's weight sits and, as REI puts it, where you can cut the most. The usual advice is to lighten the shelter and sleep system first and choose the pack last.

Section hiking

Section hiking is completing a long trail in pieces, one stretch at a time over separate trips, rather than in one continuous push. The Appalachian Trail Conservancy counts anyone who finishes the whole trail in more than 12 months as a section hiker, and recognizes them as 2,000-milers alongside thru-hikers.

NOBO and SOBO

NOBO and SOBO are thru-hiker shorthand for northbound and southbound, the direction someone walks a long trail. On the Appalachian Trail a NOBO starts at Springer Mountain in Georgia and finishes at Katahdin in Maine, and a SOBO walks the same 2,000-plus miles the other way.

Slackpacking

Slackpacking is hiking a stretch of a long trail with only a daypack while someone else moves the rest of your gear, usually a shuttle that drops you at one road crossing and collects you at the next. You still walk every mile; you just sleep indoors and carry less.

Naismith's rule

Naismith's rule estimates how long a hike will take: one hour for every three miles of distance, plus one hour for every 2,000 feet of climbing. A Scottish mountaineer wrote it in 1892 for fit walkers taking short halts, so most people need longer.

By Tom · Last reviewed August 13, 2026. Back to the glossary