Usually called a "bottleneck episodes" because the characters are trapped in a room together. So much of the episode is dialogue based.

I love how this became an actual artistic niche, instead of simply being a means to cut costs.

Thanks! I was wondering too.

Alternative tvtropes link, since that's where I thought to look: https://tvtropes.org/pmwiki/pmwiki.php/Main/BottleEpisode

It's never too late 😊

Fantastic episode 🩷

TWELVE? Twelve years old? You lost your virginity when you were twelve?

Yeah.

Twelve? You can't have been a full member of the golf club then!

Midnight, from a few seasons later, is my personal pick. The Doctor is there the whole time, but he's just stranded on a bus with a few strangers. Great example of that "nothing is scarier" type of horror.

Blink is great, but it is not a bottle episode.

Edit: I stand corrected. Abed led me to believe a bottle episode happens in one place, but it's any episode designed around minimizing cost.

https://allthetropes.org/wiki/Bottle_Episode