In reply to Robert Durran:
> I'd be interested to know what the defining characteristics are which make trail running clothes distinct from fell running clothes. Or even just from running clothes.
There's basically a blurry line in between trail, fell, mountain and ultra distance running and some people feel strongly that they're one and not the other. In my experience you can, depending on your interpretation, become virtually all of these within the space of a single run, especially somewhere like the Lake District where you will almost inevitably run on some trails, some fells, some mountains (depending on how you define a fell vs. mountain) and - if you run for long enough - it'll likely be ultra distance too.
In terms of what this means for what makes them distinct? Whilst there are some specialist products out there for each discipline, there are a lot - such as the ones on review here - that are suitable for all of them. I guess what might them more distinct from your average running clothes is that the rigours you're likely to experience road running don't compare to those you'll experience up on the hills in winter - hence you require more of them.
Post edited at 16:32