Gameplay is one of those tricky things, very hard to describe, but hopefully I can describe it for you.
To be exact gameplay is a set of rules that is enforced on a player, so that the players can have fun, why is this fact important? Since without the rules there is nothing for the players to push against for them to compete against one another.
Since I said they were rules I guess they must be definable yes? Well yes, but there’s so many rules that it would be impossible to list them all, and just because they are defined, doesn’t mean they cant change, the beauty of gameplay is that people can add and take away what they want, change existing rules slightly and so forth, all so that some variety can be added to a game and make it more fun.
But the question is do we design games, or do they just pop up in our heads, most likely the latter, so many things that we do are easily changed into games, just tells us that as animals human beings are much like otters, dolphins, apes and such. All intelligent creatures create games because they are stimulating. So as you can see its pretty important, or at least when we were walking on all limbs and went “Ug”. Nowadays, games are just for pleasure and unlikely to enhance our intellect like they did before.
So is gameplay really needed? Well it would be a boring world if it weren’t around.