These are pieces I've created digitally for the purpose of being used in games, which are commonly referred to as "sprites". Art pieces for 2D games are often displayed in sprite sheets, which will show each individual frame of animations.
Character sprite sheets will showcase the characters from every angle they will appear in, as well as any animations they may have such as running, or performing certain actions.
Environmental sprite sheets will showcase individual tiles that, when put together, can be used to create maps and environments for players to play on.