ear point (mimi) is a point horizontally one space away from opponent's stone on the fourth line or higher (most usually a one space jump stone). If the stone is on the third line, similar approach move is a check (tsume).
In the diagram, is one of ear points of Black's marked stone. In this case, it works as a keshi (reduction) to Black's framework.
If you occupy both ear points, you can cut the one space jump (or shut in the Black group) starting from .
Black's further one space jump can be cut off by sacrificing a stone at . Note that the marked White stone serves as a good peep. Safer for Black is a diagonal play at or instead of .