A perspective that is in between being viewed from the side and from the front. As seen here: https://emptyeasel.com/wp-content/uploads/2016/09/how-to-draw-a-portrait.jpg
From wikipedia:
The subject's head may turn from "full face" (front view) to profile view (side view); a "three-quarter view" ("two-thirds view") is somewhere in between, ranging from almost frontal to almost profile (the fraction is the sum of the profile [one-half of the face] plus the other side's "quarter-face";[5] alternatively, it is quantified 2⁄3, also meaning this partial view is more than half a face).
Do not use this tag for Comics where everything is viewed from multiple angles.
https://en.wikipedia.org/wiki/Portrait_painting#three-quarter_view