The term trail running literally refers to running on trails. Trail running means running off-road, away from paved roads. You can find suitable terrain basically everywhere. Be it in a city park, on a forest path in a nearby forest or in the mountains. The aim is to be out and about in nature, to switch off and leave the everyday noise behind you, at least for a while.
Trail running is often mistakenly equated with related mountain running, in which runners gain metres in altitude while carrying as little equipment as possible. Due to the sometimes considerable number of metres in altitude, runners like to use poles for mountain running, which enable better power transmission by taking the shoulders uphill. Trail running, however, can be done anywhere - whether on the flat, in the mountains or cross country.
Essential when running trails is suitable footwear, which differs from its counterparts - the classic running shoes for asphalt - in various ways. Trail running shoes must offer you support on many different surfaces, because these can change constantly during trail running: Sometimes you're running on gravel, sometimes on wet meadows, and then again on root paths through the next patch of forest. That's why trail shoes are characterised by a much more biting sole that gives you enough grip when running on gravel, stones, mud or rocks. The upper material is also much more robust so that it can better withstand contact with roots, rocks and the like.