[flashy]

What does 'F.A.B.' stand for?
Nothing! Despite appearances, as used by International Rescue in Thunderbirds, 'F.A.B.' is not an acronym - it is simply a call sign like 'Roger' or 'Ten-Four' to acknowledge received instructions. At the time of the series' production, the term 'fab' was in common usage as a shortened form of 'fabulous' which, of course, everything was in the Sixties. The phrase has enjoyed a resurgence in usage in recent years and 'F.A.B.' itself entered the English dictionary for the first time in 2002:
"'F.A.B. interjection British informal an expression of agreement to, or acknowledgement of, a command [from British television series, Thunderbirds]." - Collins Dictionary (2002)