Thunder birds what does f.a.b mean?

Fully Advised and Briefed

"F.A.B." was what each character said at the end of any radio transmission, to acknowledge the instructions were received. Of course, this caused viewers to speculate what the letters stood for, since they never revealed it on the show.

In fact, F.A.B. didn't stand for anything. In 1965, the hot "buzzWord" in Britain was "Fabulous", or "Fab" for short (ever heard of the Fab Five? Get it now?). Gerry Anderson decided that would be International Rescue's special sign-off, and even named Lady Penelope's Rolls-Royce "FAB-One".