In the original CHERUB series the children work for a secret espionage group called CHERUB. It is stated a few times throughout the books that whilst they believe the name is initials no one actually knows what they stand for now. However, in the Henderson's Boys spin off series we find out that the organisation is called (correct me if I'm wrong as it's been years since I read any of these):
Charles Henderson's Espionage and Research Unit B
It always struck me as this was just a convenient way to name the group as an afterthought for not having thought of it in the first place. However, the name also makes some sort of sense so it could have been thought of initially.
It always struck me as a bit odd that no one could have worked out at least part of the name mind you. I mean surely they know who the founder was, there's the first two and they are still an espionage and research group so surely they could have worked those out. It's only the Unit B part that would have been difficult to work out.