Maybe everyone already knew this and I'm the only person that didn't know about it...
But just on a whim, I said "Alexa, play 106.5FM on kitchen" to the Echo in my office. Lo and behold the Echo Show in the kitchen began playing the station I requested. Then I said "Alexa, stop kitchen" and the Echo Show in the kitchen stopped playing. This could really come in handy because last night I wanted to play some soft music while sleeping. But for some reason, the Echo Dot in the bathroom heard me instead of the Echo on the nightstand next to me. It was playing rather loud so I would have to scream for the Echo Dot in the bathroom to hear me saying stop. I just got out of bed and unplugged it. Having just discovered commanding other household Echo devices, now I could just say "Alexa, stop master bathroom."
FYI each of my Echo devices is appropriately named for the room and they are located in. E.g. kitchen, master bathroom, office, dining room.