Preventing the bamboo joint
There are many instances where preventing the bamboo joint like this is a devastating technique. See for example Cutting the trapezium.
Tamsin: James Davies calls this the Slapping Tesuji. There is also a well-known proverb that says "grab the fourth point of a bamboo joint".
Alex: This tesuji is also often a clamping tesuji as well, as it can be particularly devastating in conjunction with a stone at the circled point, aiming at the wedge of a.
Bill: It is often a kosumi-tsuke and sometimes a hane.
Diagrams like this drive me nuts!
Bob McGuigan: This move almost never happens without other nearby stones being involved. Here's an example from Rescue and Capture by Yang Yilun:
The Black move at captures at least five white stones, killing the white group at the edge. Of course in this case it's a warikomi.
unkx80: Compromising the bamboo joint is also seen in the following joseki.