Metadata is “data about data”, so if your post is the data, the author, when it was posted, which community it was posted in will count as it’s metadata.

Torrents are a way of distributing files between computers. Without going into the details, everyone who downloads (leecher) also ends up being an uploader (seeder). Compared to “traditional” direct downloads this makes it both faster (as you can download different parts from multiple uploaders at the same time which makes things a bit more efficient) and more resillient (as anyone who has a complete download automatically adds one more source you need to get rid of if you want that file completely taken down)