Enemy

An enemy, for the purpose of combat targeting, is:
 * 1) Any mob (or their pet) with which you have less than friendly faction reputation (neutral, unfriendly, hostile and hated).
 * 2) A PvP flagged player (or their pet) of the opposite faction.
 * 3) Any player (or their pet) you are currently dueling.
 * 4) Critters. Those poor squirrels.

Note that it is possible, through reputation changes, for friendly NPCs to become ememies and vice versa.