What is this large room with an assortment of monsters, a swarm of bees, and some items?
Solution 1:
Your instinct to check the list of special rooms was very well-founded, but what you've found is referred to as a "special level," since it's not really just a room.
What you've found appears to be the Big Room, which is generated in 40% of games, and will always appear between Dlvl 10-12 if it's present. Particularly, you seem to have found variant #3:
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As the wiki page mentions, the Big Room can be very dangerous, because the room is populated with lots of creatures and few walls, meaning that those creatures will often able to see you as soon as you enter the level, and may begin rushing towards you. Conflict and, of course, Elbereth can be very useful here.
If you entered the room through a pit or trapdoor and therefore aren't sure about where the stairs are, you may want to consider digging through the floor to escape if you're feeling uncertain; you can always come back later on better terms.
Solution 2:
This is not a room, but a special level (all of the rooms you mentioned are much smaller and make up just a part of a level (like a normal dungeon room).
The one you have found is the Big Room. Since there aren't any walls, all the monsters will spot you as soon as you appear, and start rushing towards you. I would stay the number one strategy is to stay near the stairs so that you can easily escape if it gets too much.
Other than that, you'll get a lot of use out of wands (since you'll probably hit multiple monsters), directional spells (same reason), Elbereth and rings of conflict.
Teleporting can also be quite handy if the monsters have all gathered in one spot (around you), even without teleport control.