Its been posted several times in the past, but because people are still confused:
There two types of targeting:
1) What used to be spearing, which is striking with the crown of the helmet (6 inch circle around the very top). Doesn't matter who what or where, this is always a penalty.
2) Striking with forceable contact a defenseless player in the head or neck area.
a) Defenseless players are: (1) passers during/after a throw or in a throwing stance, (2) receivers in the act or shortly after a catch, (3) players currently in the grasp of a tackle, (4) kickers and punters during/after whichever act, (5) the player who was lined up in the typical QB position after a change of possession, (6) any person being blocked from the blindside.
b) Forceable contact is contact beyond what is required for a normal tackle (putting a lick on someone) which must be accompanied by an indicator of targeting: launching, upward thrust, forearm shiver, leading with the crown or shoulder, kick or punch.