The word gameplay gets thrown around alot out there, and probably has a hundred different definitions. So I'm going to make it a hundred and one by trying and describe what I think the term gameply means.
Every game has rules. If a game had no rules it wouldn't really be able to exist. For something like a game to function properly there have to be boundaries, places you can't reach, things you
can't do. We also need to be told what we can and can't do in a game. Different game genres usually have set rules, for example, a racing game has a track. This is the track you race and you have to stick to it. Of course people try to expand these rules, by letting you take different paths of giving you the illusion that you can go where you want, but they generally still stay the same.
Burnout Paradise did this by giving you a big city and letting you go where you want. But utimately it was just a bunch of tracks duct-taped together. You were still confined to a track and were still made to go a certain route if you wanted any chance of winning.
I think this is all relevant in the term gameplay. There are other more technical sides to it aswell, such as, what button does what and how much damage this gun does.
I think if I had to sum it up (which is incredibly difficult and probably unaccurate) I would say that gameplay to me, is the game designers giving us decisions to make. For example, how do i approach this battle, what weapon should I use for this situation or how early should I apply the brakes if I dont want to crash, unless I want to crash and see the car deform and explode, which happens all to frequently when playing Burnout.