Video jack on vintage TV?

[CaryLee]

I never really thought about it before..

I understand a PHONO jack on a vintage TV. Just like a vintage radio, one can hook up an electric phonograph and play sound through the TV's amp and speaker.

Perhaps the answer is so simple I'm going to kick my own butt when someone mentions it, but my vintage (1950) TV has a VIDEO jack right next to the PHONO jack.

What did they have, in 1950, that would require a VIDEO jack on a television?