defensive techniques. The peter and the tenace
I have listed a couple of other useful defensive techniques here but there are many more that you will come across when you play on a regular basis.
A very useful, and simple technique for communicating with each other when defending a contract is the peter or echo.
Your partner leads to a suit contract and you only have two cards in the suit and can trump the third round. How to tell partner? On the first lead of the suit you play your higher card and follow this the second time the suit is led with you lowest card of the suit. The message is "partner, lead them again". Conversely playing low and then high tells you partner you have more than two in that suit.
It goes without saying that you and your partner must both agree to this system and watch out for each other's discards during the play.
The tenace
Nothing to do with tens or aces! A tenace means broken strength such as that shown here. An ace/queen as shown or a king/jack or even an ace/jack are collectively described as tenaces.
It is nearly always a good idea to lead through broken strength and if you are leading to the dummy you can see if there are any tenaces in that hand. Let's suppose you see the ace and queen.
Having established that, you lead a low card and the hope is that either that declarer will play the queen enabling your partner to beat it with his/her presumed king or will play the ace making your partner's king master.
Of course it doesn't always work because the declarer may have the missing card but if you partner showed interest in that suit during the auction you stand a good chance. In effect, this technique is the exact opposite of a finesse