The meaning of Fill out

phrasal verb

Write all the required information onto a form

phrasal verb

(of a person) put on weight to a noticeable extent.

Usage examples:

He had filled out since the last time i'd seen him

phrasal verb

Add information to complete an official form or document.

Usage examples:

He filled out the requisite forms

phrasal verb

To become larger

Usage examples:

When john is older and fills out some, he’ll be an outstanding athlete.

phrasal verb

To write or type information in spaces that are provided for it

Usage examples:

The 9m taxpayers obliged to fill out self-assessment forms must file their returns by september 30.