A loud, percussive orchestral hit sample, used annoyingly for no reason in 80s pop music.
The word is
http://www.m-w.com/cgi-bin/dictionary?va=onomatopoeic, since the hits sound sort of like
fwank! Most notable examples of use: Owner of a Lonely Heart by Yes, and Unforgettable Fire by U2.
80s pop music can be dated by the sheer number of fwanks used per song.