The stochastic background of gravitational waves produced during the creation of the universe. / The irresolvable diffuse background resulting from the mixture of weak gravitational waves of all sources.

Alternative form of kick up the arse

plural of kick up the backside

(US, journalism) The status of information acquired from a source that may be used, but without either naming or directly quoting the source.

plural of backdoor pilot

Alternative form of back-door pilot

(UK) A proposed seamless border between Ireland and Northern Ireland in the event of Brexit.

Alternative form of think the sun shines out of someone's arse

(humorous) One who takes something back, especially one unfairly demanding the return of a gift previously given.

Alternative form of back-seat gamer.