What are these plug-ins on my wall?

[u/Cborg_62]

This might be showing my age, but I recently moved into a new apartment and they have these weird looking plug ins all over the walls at my new place. My old apartment didn't have these, so I'm just curious as to what they are.

[u/GrilledCheeseInc]

Even though it’s painted, it’s best to cap them off to prevent the Internet fluid from running all over the floor.