smaller human
This is used when two (or more) beings are together and the smallest one happens to be a human compared to an anthro character, a feral animal, et cetera who is also present. This is typically used for couples with a notable size difference but can be non-romantic and non-sexual. The opposite situation is labeled larger human.
See also:
Larger
Gender
Smaller
Form
Gender
This tag implicates human, size_difference (learn more).