1
general::
A word or gesture of support, approval, or praise, as in The bonus she gave her assistant was a pat on the back for doing a good job. [Early 1800s]
American Heritage Idioms
2
general::
Phrase(s): pat someone on the back [and] give someone a pat on the back
1. Lit. to pat someone’s back to show praise. • The coach patted each player on the back after the game. 2. Fig. to praise someone for something. • The teacher patted all the students on the back for their good work. • They were patting themselves on the back for winning when the final whistle blew.
McGrawhill's American Idioms And Phrasal Verbs