Game Assets

Definitions of an asset

"Things you own"
Link 1

"anything of material value or usefulness that is owned by a person or company"
Links 2

Definitions of a Game Asset

"artists develop game assets such as sprites or, more often today, 3D models of game elements"
"Game assets are the "things" that go into a game"
"Sometimes the terms content or objects are used interchangeably with the term assets."
Wikipedia

"Game assets are everything that contributes to the visual appearance of the game"
"from the drawing board into production, where concepts materialise into game assets"
Link 4

"game assets, which are the collection of data files used to support gameplay such as bitmaps, models, textures, or sounds"
Link 5

In my opinion game assets are basically everything that makes up a game that supports the gameplay. They include everything you can see and hear, including both basic and complex character animations, facial expressions, skins, textures and many more things. Games assets are also associated with content, which backs up the idea of games assets being everything you would need to support the gameplay. Without assets a game wouldn't be anything.