1. flip the bird - Verb
2. flip the bird - Phrase
(colloquial, idiomatic) To make a rude or obscene gesture (at somebody); particularly, to extend the middle finger.
Synonyms: flick off, flip off, give the finger, give the bird
I accidentally bumped into him, and he flipped me the bird.
Used other than figuratively or idiomatically: see flip, bird.
Source: en.wiktionary.org