Pictures of the same character repeatedly in the same image, either copied and pasted or redrawn, with minor variations such as changes in outfit or hairstyle.
This should be differentiated from sequential actions, such as a frame-by-frame rendition of a dance, or the stages of creating an illustration (sketch, inking, color, etc). The latter should be how to. This also does not include comparisons between different characters or different characters wearing the same outfit.
Not to be confused with variant set, which refers to a series of images depicting the same scene with some differences.