Cutter is a term referred to a delivery that cuts off the seam after pitching. Off cutter is the one that cuts into the batsman after pitching (all references made with regard to a right hand batsman). Unlike an inswinger which swings in the air before coming in, a off cutter does not swing in the air. It basically cuts into the batsman after pitching.
There is a pronounced employment of the finger in the execution of a cutter. However, the methods used differ from bowler to bowler.