transitive verb
Definition 1
Complete, add, enter (all required or appropriate details, information, etc. in spaces provided in form or similar).
Source: Invertext
Context: Please fill out the form below and send.
Source: docstoc.com
Definition 2
Expand (thing) to its requisite or desired size or shape.
Source: Invertext
Context: Mama made me drink a glass of milk each night in a vain attempt to help fill out my dresses in the right places.
Source: fanfiction.net