reinforcement

Short definition from Wiktionary

Noun

1. 1
   The act, process, or state of reinforcing or being reinforced.
2. 2
   A thing that reinforces.
3. 3
   Additional troops or materiel sent to support a military action.
4. 4
   The process whereby a behavior with desirable consequences comes to be repeated.
5. 5
   A small round white sticker placed around a punched hole in a piece of paper to prevent the binder's rings from tearing through the paper.