I've seen some Projects where something like this was written in the credits: “Thanks for curating this, scratch team” I read that and wondered what it means a Project is curated. Please tell me!

If it is “curated by the Scratch team,” I guess that means the project was featured.
If it's curated by someone other than the Scratch team, that means it was selected by that person to be on the front page. Read the Curator wiki page for more info.

Thanks for explaining!