goalpost

noun

Etymology: From goal + post.

1. One of the two vertical side poles of a goal.

   “Some kids were having a kickabout on the grass beside the walkway, cheering, groaning, calling for the ball, absorbed in the game, a self-contained universe marked out by jackets for goalposts and invisible touchlines.”

2. The tall Y-shaped upright, now usually of fiberglass, at either end of the playing field, through which a football must go in order for a field goal to be scored. (They were originally H-shaped, with one wooden post on either side.)
3. A rule or target that is "moved" (changed) unfairly; see move the goalposts.

   “[…] whatever you eat, how much you drink, you know the goalposts keep moving all the time, and it's difficult to be sure that, but I don't think it's harmful, not the amount I drink.”