Losing trick count is a form of hand evaluation where you count the number of losers in each suit, to a maximum of 3 per suit. So
- A, AK, AKQ, AKQxxx, and -void- are all 0-loser suits.
- x, K, Ax AKx, AQx are all 1-loser suits.
- Qx, xx, QJx, Kxx are all 2-loser suits
- Jxx, xxxx, xxxxx, are all 3-loser suits.
Note that 3 little in a suit is the worst possible holding -- it counts for 3 losers without covering any losers in another suit.
Losing trick count is a bit controversial -- note that Qxx xxxxx Qxx xx evaluates to 9 losers, as does AJT AJxx xx Jxxx, where the second is a far stronger hand. However, losing trick count is probably more accurate than high card points when evaluating a distributional hand that has a fit with partner.
The scale of evaluation is based on the assumption that when you add your losers to partner's and subtract that number from 24, you'll make that many tricks. So a 7-loser hand is a minimum opener / game force. An 8-loser hand is invitational and a 6-loser hand accepts. A 9-loser hand is a typical responding hand.
Most players I know only use losing trick count to make decisions when they know that they have a known 9-card fit or double fit with partner (or possibly a 4-4).
On the other hand, I wouldn't worry overmuch about 3 small in a suit. Often partner will have an honor or shortness to make the suit less hopeless. Another way you can avoid bad games with 3 small is to be on the lookout for wastage; when you have cramped honors in a suit (e.g. KQ tight, AQJ, etc) and partner shows a stopper in that suit, that's bad news -- it means that you're double-counting the honors in that suit.