It's my fault, I was super confused.
The "blue" ones are "Categories". They themselves don't hold any "threads".
The sections under the "Categories" are forums / sub-forums.
So, using your example:
Chicken breeds = Category
"What breeder gender is this" and "the general breed discussion and...
They have a ton of names. LOL!
Technically (at least with the software we use) they are referred to as "forums".
The structure of the forum is basically:
NODES:
-Forums
-Pages
I often just call them "sub-forums" since I (personally) refer to the entire section as the "BYC Forum".
... but...