3bet vs. 4bet

[Zacanic]

I'm a little confused with some of these stats although I appreciate the logic in most of them. What's the difference between a 3bet opportunity, & a 4bet opportunity? If a situation arises that is a 3bet opportunity, is it not a 4bet opportunity as well? The stats I have in Poker Tracker show that you a significantly higher 3bet opportunity total than you do a 4bet opportunity total. Can an Einstien please explain this to me.
Thanks abunch,
Jo Mama.

[WhiteRider]

PT2 doesn't have 3- or 4-bet stats so I assume you mean PT3?
A 3-bet is the third "bet" (or the second raise), so preflop the BB is the 1-bet, the first raise is a 2-bet and the first re-raise is a 3-bet. In PT3 any further raises are 4-bets.

[Zacanic]

Your clarification makes all the sense I never had.
Thanks for your help.
Jo Mama