Multiple states of a UI element in one image file. How's that called?

Question

I heard that it is common practice to have multiple states of an UI element like a rotary knob or slider in one wide JPEG/PNG file.

From what I know this is mainly used when designing super realistic UI elements so that all shadows and reflections are correct.

I would like to look into this a bit further but I'd need to know how this practice is called. Anyone got a hint?

Answer 1

a 'sprite' is the term you're looking for.