A double pass
is when Player A passes the ball to Player B (a soft pass) to draw the player (and his/her defender) toward Player A. Player B then one touches the ball back to Player A (on an angle to allow for success on the next pass) and then Player B spins away. Player A then plays the ball into the space that Player B is running into (which is going to be behind the player defending Player B.) This is a penetrating pass into space for Player B to run on to.
One of the keys to the double pass is for Player B to make a run back to the ball and also be able to hold the defender off. Then Player A should play a SOFT pass into Player B. The reason this ball should be played soft is that you WANT to draw the player marking Player B to think he/she can get the ball. By checking back like this, you open up the space for the penetrating pass.