(Internet slang) secret personal account (on social media, especially Twitter and Instagram (finsta), as opposed to one's openly used account)

back and front; both sides / inside out / disparity between appearance and true qualities; two-faced / ins and outs

(music) syncopated beat, an accented part of a rhythm marked by syncopation

empty theory; an armchair theory

back page; back cover

fortune cookie

leap second

hooray! (in the context of Russia or the Soviet Union)

to outwit; to defeat with the unexpected

wolf cut (heavily layered hairstyle)