Functional movement actually lacks a universal definition, which really complicates matters.
But . . .
One classic definition for functional movement is that it’s movement with “real-world carryover”. Functional movements help us perform daily life tasks better. (Or sport-specific tasks if we’re an athlete.)
By this definition, many people consider “pretzel”-like yoga poses, deep ranges of motion, and passive stretching to be non-functional, and they update their yoga classes accordingly.