What does FAB mean in thunderbirds?

The characters use the radio sign-off "F. A. B." rather than "Roger" or "Over and out". Anderson was often asked what F. A. B. stood for, but in fact it simply stood for "fab" (short for "fabulous"), which was a 1960s catchphrase. Later this was unofficially decided to mean Fully Advised and Briefed, following on from P-W-O-R (Proceeding With Orders Received), a similar radio confirmation code in the series Stingray.