I would like to chime in here cause I remember having an interesting conversation with a local dealer on this very thing. Playing live several of us at the table (3/5 NL) were discussing a particular play and possible outcomes. We were using the 3bet 4 bet lingo to refer to the raise/reraise/rereraise that had occurred. The dealer said that there are no 3 or 4 bets in NL poker and he and I were off on a debate over the rest of his time in the box.
The thing is that the terms started up several years ago on the strategy forums among, mostly, internet players. When they refer to the 2, 3 or 4 bet in a NL game the amount of the raise is irrelevant. It is simply referring to the line of betting: one raise after another. In limit poker, it is essentially the same thing only difference being that the bets are a fixed amount.
I am going to have to disagree with MikeB in his description of the all in wager presented by michaelgtjr. If there is a bet of 50 by player A and player B Raises 75 to 125 then there is an all in totaling 175 it is not a wager but an incomplete raise/all in. So if there is a player yet to act behind this all in player that player has the option of calling the 175 or reraising the original raiser and, I think, the amount of the raise only has to be 75 to a total of 200. He is not technically "completing' a raise by the all in guy but doing the raising himself because the all in guys all in is irrelevant. See RROP section 14. TDA 31 refers to the previous "Legal" bet or raise. Now if there are just the 3 players and action is back to player A after the all in all options are open, raise to total of 200, call the 175, fold. If Player A just calls then player B can ONLY call the 175 or fold, a raise is not open to him because the all in is not a legal raise and player b can't raise himself.
edit: hope that isn't too confusing. let me know and I'll try and make it clearer. All I'm saying MikeB is that the all in amount doesn't effect the next minimum amount that any other player yet to act has to raise.