A queen cup (a.k.a. a cell cup) is a cell the bees build in case it becomes necessary to create a new queen in a hurry, and it can look like this:

That’s what a fresh queen cup looks like on new plastic foundation. Here’s a better shot from an old post called Queen Cups Are Not Swarm Cells:

Drone cells poke out in a manner that Americans say look like bullets, sort of. Queen cups are more rounded. They poke out and are open on the bottom. Here’s a few of them clumped together, maybe mixed up with some drone cells:

I noticed several of these queen cups during inspections yesterday. Queen cups become swarm cells when a colony is ready to reproduce or supercedure cells when the old queen is dead or injured or failing and needs to be replaced. The presence of a queen cup doesn’t mean any of that will happen, though. See Is it a swarm cell or a supercedure cell? at Honey Bee Suite for more info.