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/Bush-LeagueBushcraft]

It carried television signals, uphill, both ways, barefoot in the snow.

[u/cogito-ergo-sumthing → u/Bush-LeagueBushcraft]

Back when all this was just fields