Lavinthal Discards (McKenney Discards)

Lavinthal discards are used at a defender's first opportunity to make a discard. A high spot card is suit-preference for the higher of the two remaining suits, whereas a low spot card is suit-preference for the lower-ranking suit.

For example, imagine that declarer is playing on diamonds and you must make a discard for the first time:

A club discard discourages clubs. There are two "remaining" suits: spades and hearts. Therefore, a high club is suit-preference for spades (the higher of the two remaining suits), while a low club is suit-preference for hearts.
A heart discard discourages hearts. A high heart is suit-preference for spades, while a low heart is suit-preference for clubs.
A spade discard discourages spades. A high spade is suit-preference for hearts, while a low spade is suit-preference for clubs.

Lavinthal discards are very similar to Revolving Discards. The difference lies in which suits are encouraged by a high or low discard. Playing Lavinthal, for example, a low club discard is suit-preference for the lowest of the two-remaining suits. Playing revolving discards, a low club is normally suit-preference for spades, the "lower-ranking" suit.