Sprite sheet

A sprite sheet is an image with a sprite’s expressions/poses, usually used with a game or animation engine for composite/multi state sprite optimization. Packing sprites into a single sheet optimizes file load and render time in many cases where it's needed.

In visual novel terms, it may also refer to an aesthetic layout of a character sprite’s images that shows the different poses/expressions of a character, usually for inclusion in the game’s art book or for promotional purposes (ex: crowdfunding graphics).