$EV is short form for Expected Value or chip-EV
It is the average number of chips you expect after an action. The EV will tell you the number of chips one will have earned or lost after an action.
There is the $EV which is important for the ICM and it is the monetary value of the EV. You do not convert your chips to liquid cash during a tournament but your aim is to rank as high as possible. The $EV assists you in getting to know how the action will affect the expected value and grow your ranking.