Is usually found in power cords, but I digress. Usually the outlet corresponds to the voltage delivery system. At least you hope that that is the way it is. Back in my 3rd form days (a LONG while ago), the place I was schooled at we VERY "british" for being in the USA. A couple of older buildings were actually wired for 240 volts (yes, they were VERY old). Since everyone knew what to expect, transformers abounded for such mundane things as record players, and refrigerators (very big transformer). We didn't have much other stuff, as this was decades before PC's. I was tasked to make a recording with a nice reel-to-reel tape recorder in a place that I didn't know was a 240 volt building (ooops!), and promptly blew the fuse. The outlets were the same as the 120 volt power elsewhere, so I didn't know. My clue was that the light bulbs were 240 volt, so I quickly got another tape recorder and did my work. I suppose someone else changed the fuse.
Ah, youth. Yes, it was over 50 years ago.
In my garage, I do have a nice 240 volt outlet, and it has the proper NEMA 6-15 socket that has the horizontal blades, not the vertical ones for a 5-15 outlet normally used. Yes, it is labeled 240 volts as well!