A keima is also called a knight's move. A kakari is an approach (or attack) on a single corner stone.
So, a keima-kakari is a stone that approaches a corner stone by being a knight's move away.
It is approaching the single corner stone low, on the third line.
White 1 here is a keima kakari. A keima kakari is often used to approach a hoshi stone, as it is flexible and can respond to whatever Black does (unlike an invasion at the 3-3 point which is very limited).
It is also a very common approach to komoku.
See also