Suction
Defense against 1NT opening:
suit overcall shows either
1) the suit above it, or
2) five-five distribution or better in other 2 suits
2C = diamonds, OR 5-5 in hearts and spades
2D = hearts, OR 5-5 in spades and clubs
2H = spades, OR 5-5 in clubs and diamonds
2S = clubs, OR 5-5 in diamonds and hearts
Overcaller will usually hold the long suit and not the five-five distribution.
This defense is similar to TRASH overcalls, although I believe TRASH overcalls show more strength.