The LAW of Total Tricks (LOTT) is a bidding guideline developed by Jean-Rene Vernes. It helps you to decide how high to compete, using this approximation:
With 8 partnership trumps, bid to the 2-level.
With 9 trumps--3 level.
With 10 trumps--4 level.
So, if responder to 1 holds: Q76
, and hears partner open 1, he knows his side has 8 trumps. He won't raise immediately to 2, because that would be a lie. Bids still mean what they always meant and raising to 2 shows 6-10. So, responder has to pass, but he knows that if the opponents now balance (say 1-P-P-2) that he should be willing to compete to 2 since the partnership has 8 trumps. It doesn't mean 2 will make, but even if it is down, that is likely better than defending against 2 (likely making).
Similarly, if responder to 1 holds: Q 8 7 6
K 8 7 6 4
, he knows his side has 9 trumps. He can't raise to 3 since that would be invitational. But, later, if he has to, he should compete to the 3-level (1-P-2-P; P-3-3).
With 5 trumps, responder to 1 will raise to 4 (which is defined as 5 trumps and weakish). Example: KJ876
Over partner's 2-level preempt (6 cards), be willing to compete to the 3-level with 3-card support (9 total trumps) and the 4-level with 4-card support (10 total trumps). After a 3-level preempt by partner, assume a 7-card suit and use the LAW accordingly.
Use LOTT only when you don't have game or slam interest.
Never Lie (1-2 means what it has always meant).
Use the LAW mostly on the 2-3-4 levels (not on the 5-level or higher).
The "LAW" states that on most bridge deals the total number of trumps is approximately equal to the total number of tricks.
There are 4 articles on this website with more details, as well as a brief description of 3 books by Larry Cohen on the LAW: