How do you define a cafeteria-style restaurant? Bad food buffet?

No.
How do you define a cafeteria-style restaurant? Bad food buffet?
American cafeteria restaurants are much like the ones we have in our schools...but generally better.
So, you enter, grab a plate and utensils, and either get in a line or go to certain serving stations where food is being served to you by employees. Usually, the food is resting in a steam-table or under a heat lamp, much like you'd find at a hot buffet. Some things are also kept chilled.
American cafeteria restaurants are much like the ones we have in our schools...but generally better.
So, you enter, grab a plate and utensils, and either get in a line or go to certain serving stations where food is being served to you by employees. Usually, the food is resting in a steam-table or under a heat lamp, much like you'd find at a hot buffet. Some things are also kept chilled.
Where I am, they have as many strata of cafeterias as standard restaurants. There are some that are definitely just barely a notch above institutional food, while others are darn near being fine dining. One near my house used to serve prime rib and lobster...*.
Lately I've been wondering how common peanut butter is outside of the US.
I forget...did I mention pocket-sized powdered or liquid drink mixes?
The last time my parents went abroad in 2010, my Mom's use of such things at the table was so unusual that a chef actually came out to see what she was putting in her water or tea...and was quite thankful when she gave him a bottle.
And when she was on the return leg, she left her stash with the hotel's cleaning lady...who said she was going to call her family to share the bounty! No, she wasn't being sarcastic.