Grab your trail and squeeze
(1) A slight narrowing in the trail tread usually because of rock or logs. Sometimes deliberate, when used to control user speed. A "choke point". A "choker". A "gateway".
For example, a series of logs might be staggered on opposite sides of the trail to narrow the route. This slows trail users at scenic points or before dangerous areas. The narrowing should blend into the trail naturally or users may simply go around it. On multiple-use trails, a choke slows faster travelers like cyclists in congested areas, and can help to avoid injuries or conflicts among users.
(2) A narrow place in a trail where your competition gets scraped off (if you are still in that elite and crazed group trying to set land speed records on foot).
(3) Otherwise, it's a place (possibly natural) where you need to slow down and go in single file (if you've learned to play nice). Remember, nice guys finish last. And so do losers.