Something very pleasant, beneficial or useful, often received unexpectedly and without being deserved.
A thing that reinforces.
The process whereby a behavior with desirable consequences comes to be repeated.
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.
Additional troops or materiel sent to support a military action.
The act, process, or state of reinforcing or being reinforced.