There is a Canadian Carnival. There is a Christian Carnival. There is now a Catholic Carnival.

Carnivals are weekly or bi-weekly collections of blog posts.
They are self-submitting, which makes sense. A blogger has an opportunity to showcase a post they like on another blog so it will be more widely read.
A carnival is a collection of submissions hosted by a blogger - who has the server space, or is sometimes hosted by different people from week to week.

Having said that, I’ve never submitted a post to a carnival. Some personal quirk I guess, because I rather like the idea. It’s just that once I write something and toss it out, it’s ‘gone’ for me. The only time I head into the archives is to clean up spam or link to something that is being re-cycled in my thought process on a certain day. If this blog didn’t have a good search engine, I’d be sunk. And, I’m lousy at self-editing. There are times I really enjoy wrestling with my words and there are times I feel like I didn’t lose.:^)
A lot of bloggers put a great deal of effort into posts, and carnivals are a way to showcase their best.