Just like you are guessing, this is a bad guy or the enemy. Most commonly used by the aviation guys to identify a target. Ship board combat folks use the term Vampire. Pilots like to keep with tradition and use the term that has been around for so many year.

There were times when I would see one of the ships lookouts and I would hear them use the term bandit or bad guy. Never did hear any of them use the term Vampire. I suppose a vampire is a radar contact only where as a bandit is an actually visual contact with a possible enemy.

Pilots will use the term in their communications between planes as well as with combat systems. “Bandits, Angels 10, 6 O’clock. 6 Miles” or “Bad guys. 10,000 feet, behind us 6 miles.”

You can do this when driving and you see a police officer. Yell out “Bandit 10 o’clock. Give me a fire solution!” Then have your wife smack you. See I can teach you something and help make those long family drives more fun.