seeds are peers that have completed downloading the contents of the torrent (or a subset they selected) and are therefore offering uploads only. This contrasts with leachers, which are peers that are still downloading.

Not quite… In order for the system to acknowledge you as a seeder, you must have downloaded 100% of ALL the files, not just the ones you have selected.

A leecher on the other hand generally is in the process of downloading the torrent's contents. Simply put, they have not yet downloaded 100% of ALL of the contents. This count will include people who have for example downloaded the video file, but not the pictures, or users who have only downloaded some of the videos in a collection.