I recently read an article by Ordinance Survey about trail runners for beginners (my interest has sparked due to my recent uptake of running which I do cross country through parks and fields), in which is stated that Trail and Fell^ running are often used synonymously, but that they are in fact different. The difference they stated was simply terrain, one soft ground, one hard ground.
Some interchange 'trail' and 'fell' running, but the two concepts are quite different, with the latter acknowledged as far more 'rugged, rocky and extreme'.
Is there an actual difference or differences (terrain, altitude, etc) between Fell running and Trail running, as stated, or are they the same?
This would be useful to know when looking up local running routes, as I want to progress into more challenging runs.
^also apprently known as hill/mountain running