Sizeshifting

Sizeshifting (a term created by analogy with shapeshifting) refers to the changing of size, be it from greater to smaller (shrinking) or smaller to greater (growing). A sizeshifter is a term encompassing any sort of being that can change their size at will.

Sizeshifting and furry
When used in the furry fandom, it generally refers to a fursona capable of changing his or her own size. After the change (sometimes called the Shift), the fursona typically retains his or her proportions, resulting in having simply scaled up or down their image in the world. (Obviously if such a thing were possible in reality, it would violate the square-cube law)

Sizeshifters typically have a default size, representing the one they are most comfortable with.