This sort of pattern: is a contact play (tsuke) and a block (osae). This is a territorial way to play.
White normally plays immediately to give Black the so-called hat shape. Then White has to deal somehow with the two cutting points a and b. Neither side has perfect shape here, therefore.
Before is played, there was some aji at c - which disappears after . Black can play attach-block as an attacking technique, to make White heavy. When White is defending a group, the atari play is probably something that White must play.
See attach-block joseki.