A method of defensive signalling after your first play in the suit did not show your length (for example if you were covering an honour, playing third-hand-high). If you have an odd number of cards left, you discard or lead your lowest card (just as you would play low from an odd number if you were signalling length on the first play of the suit.) If you have an even number left, you play a high card.
For example, suppose you hold Q-J-6-3 and your first play is to put up the jack third in hand. You have an odd number of cards remaining, so if you lead or discard from the suit, you play the three. If a partnership’s primary discarding method is suit preference or attitude, it is also quite common to play that a second discard shows remaining count even in a new suit.
