Rusinow leads is a bridge

Contract bridge

Contract bridge, usually known simply as bridge, is a trick-taking card game using a standard deck of 52 playing cards played by four players in two competing partnerships with partners sitting opposite each other around a small table...

 convention

Bridge convention

A bridge convention is a system of calls made during the auction phase of a contract bridge game which conveys a coded meaning about the players' card holdings...

 used as part of defensive carding

Signal (bridge)

In the card game of contract bridge, partners defending against a contract may play particular cards in a manner which gives a signal or coded meaning to guide their subsequent card play; also referred to as carding.-Standard signals:...

. Rusinow leads are commonly used only on the opening lead

Opening lead

The opening lead is the first card played in the playing phase of a contract bridge deal. The defender sitting to the left of the declarer is the one who makes the opening lead. Since it is the only card played while dummy's cards are still concealed, it can be critical for the outcome of the deal...

against a suit contract.

In accordance with the convention the second highest honour card is lead from touching honours against a suit contract. So from KQ94 a player using the Rusinow Lead convention would lead the Q. This eliminates the ambiguity of the lead of the King against a suit contract where the partner of the leader may not be clear whether his partner has the Ace or the Queen.