I read that book too. It's just 'Phil-speak'. Personally, I have never heard anyone in the real world call it a 3 bet. lol.
Basically, Phil means that three big bets have been made in a given betting round. It is a significant event because, in many casinos, limit games have a maximum of 3 bets and raises for each betting round. Some Indian casinos allow 4.
For no limit games, the rule depends alot on the cardroom. Some allow unlimited bets and raises, some allow 3 or 4, and others still allow unlimited bets and raises when in a heads up situation.