What is the difference between a leech and a seeder?

The person that hosts a file in its entirety, all of the chunks, is called a seeder. This person has all of the chunks available in one location and the file swarm can grow, like a tree, from this one seed. A leech is a person who downloads files without ever seeding them. Most torrent sites want to see a positive upload to download ratio.

What is the difference between seeding a torrent and leeching a file?

Seeding is the act of hosting a torrent for others to download. Leeching is the downloading of a file hosted ("seeded") by someone else. To clarify - a seeder is not the website where you download the literal whatever.torrent file from.

Are all seeds and leeches a peer?

All seeds and leeches are peers, but not all peers are seeds or leeches. The role of a peer can change over time, evolving from a leech to a seed or vice versa, based on their actions and the state of the file they are sharing or downloading. Peers serve as the foundational units of any torrenting activity.