The difference between off-road running and trail running is really that trail running may include a short section of road that leads to the trail and the trail itself is not intensively hilly. Off-road running is the hillier stuff and is also known as fell running. It's common sense to know that you should give these things a go before kitting yourself out fully just in case you don't like it. Once you know you want to continue it's then important to get the proper kit in order to protect yourself from the elements but more importantly to avoid injury...