The term gameplay is a very puzzling one. I believe that gameplay is the term used to describe the 'playing' of a game. What happens as you play it. If a game lacks the core fundamentals of gameplay; action, drama, flow , etc, it will fall flat on its face.
The dictionary describes gameplay as the following; 'the tactical aspect of a computer game, such as its plot and the way it is played, as distinct from the graphics and sound effects.'
To put it bluntly, its how the player plays the game. I find that when I play games, I subconsciously think about the gameplay as I play. I like a game with a lot of action, as do a lot of people. But I long for something more most of the time.
I definitely think gameplay can be designed and interwoven within the making of a game. For games nowadays, some developers dismiss the fact that gameplay is probably the most important part of a game. They rely on graphics and effects alone, which really shows.
Gears of War 1 and 2 have great gameplay. The cover system and over-the-shoulder view were taken to another level in these games, as well as the shooting mechanics and effects. Overall, a great experience. It left me wanting more, which is exactly what gameplay should do.