What does FAB mean in the 'Thunderbirds' TV series?

Fabulous

http://gerryanderson.co.uk/question/what-does-fab-stand-for/

From Gerry Anderson's own site:

This has got to be one of the most asked questions: What does FAB stand for in Thunderbirds? Well here’s the answer in one simple word: Nothing! In the 60’s the buzz-word was “fabulous”. This was shortened to FAB and used simply as a call sign like ‘Roger’ or ‘Ten-Four’ to acknowledge received instructions. If it was an acronym, then the best suggestion we’ve heard for a potential meaning is “Fully Acknowledged Broadcast”. So now, next time someone asks you what FAB stands for, you can give them the authoritative answer: nothing!

According to Gerry Anderson it means absolutely nothing (not literally.)

Well per Sylvia Anderson it means Fabulous. She is the co-creator of many magical series that have become television classics: Supercar, Fireball XL5, Stingray, Thunderbirds, Captain Scarlet, Joe 90, The Secret Service, and later, U.F.O. and Space 1999.

She also played many of the voices, but it was as the beautiful superagent, Lady Penelope, in the legendary series, Thunderbirds, that she won the hearts and imaginations of a generation. The characters she developed - Penelope, Parker, and the International Rescue Team - have become cult figures and their adventures live on today.