HP-o-meter

HP-o-meter, HP-ometer, H.P.-ometer, n. an imaginary meter that floats above the heads of all creatures in a game world, and can be seen only by the DM and PCs; it allows specific knowledge of the creature's physical condition to be known to all who can see it. From hit points. Also Hit Point Meter. [MB]
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Addendum: This term may stem from video RPGs, where hit points are often measured as a bar graph - the less of the bar there is, the more trouble you're in. See chipping pixels. [MB]
GM: Aren't you going to double back and help Sir Goodalot?
Player: No, he's got 2 HP left. He'll live.
GM:' What, did you determine that using your long-distance medical triage powers, or did you just look at his HP-o-meter? Stop metagaming, and go check on Sir Goodalot! 
Player: Damn it. I'm never playing the cleric again.