DuckCorp Dico

Found one definition

1.                 From WordNet (r) 3.0 (2006):
                   
   
   
                   
                     
   fill-in
       n 1: someone who takes the place of another (as when things get
            dangerous or difficult); "the star had a stand-in for
            dangerous scenes"; "we need extra employees for summer
            fill-ins" [syn: stand-in, substitute, relief,
            reliever, backup, backup man, fill-in]