Roleplays here generally take place over one thread, though that thread can be hundreds of pages long. You can think of there being two types of roleplay:
1:1 roleplays are for two people and the plot is typically contained to one thread. 1:1 RPs are a great way to make new RP friends or to just casually play with an idea!
Group roleplays are for more than two people! Found a group who wants to see the same plot unfold? Do a group thread!
A thread that starts out with the idea of a 1:1 does not have to stay as a 1:1. you are welcome to invite more people to join.