fill out (Verb) — Write all the required information onto a form. ex. "fill out this questionnaire, please!"
fill out (Verb) — Make bigger, better or more complete.
fill out (Verb) — Supplement what is thought to be deficient. ex. "He filled out his meagre pay by giving private lessons"
fill out (Verb) — Line or stuff with soft material. ex. "fill out a bra"
fill out (Verb) — Make fat or plump.
fill out (Verb) — Become round, plump, or shapely. ex. "The young woman is filling out"