Cutter is a term referred to a delivery that cuts off the seam after pitching. Leg cutter is the one that cuts away from the batsman after pitching (all references made with regard to a right hand batsman). Unlike an outswinger which swings in the air before moving out, a leg cutter does not swing in the air. It basically cuts away from 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.