What is a seeder and what is a leecher?

When I use Transmission to do the downloading, I see some figures on the web control panel of Transmission. Those are technical terms. Such as Seeder, Leecher, Ratio, Trackers, Peers, etc.

So the questions come. What is a seeder? What is a leecher?

Let me check it from search engine and put all together.

What is a seeder?

Seeders are people who have already downloaded the whole file and are uploading them. The more seeders the faster the download will go.

What is a Leecher?

Leechers are people who are sharing what they have and are downloading what you have. (It is real BT spirit here.)

What is a Tracker?

A BitTorrent tracker is a special type of server, one that assists in the communication between peers using the BitTorrent protocol.

There are BT and PT. Two types of BT. PT is one special kind of BT. It is only allowed the people with a correct passkey to connect to the tracker.

Normal BT tracker URL sample:  http://secure.pow7.com/announce
PT tracker URL sample: http://pt-tracker-server.com/announce.php?passkey=0394778bcea8a6of7db8f3e60die6d5

What is a Peer?

A Peer is one instance of a BitTorrent client running on a computer on the Internet to which other clients connect and transfer data. Depending on context, “peer” can refer either to any client in the swarm or more specifically to a downloader, a client that has only parts of the file.

What is a Ratio?

A user’s share ratio for any individual torrent is a number determined by dividing the amount of data that user has uploaded by the amount of data they have downloaded. Final share ratios over 1.0 carry a positive connotation in the BitTorrent community, because they indicate that the user has sent more data to other users than they received. Likewise, share ratios under 1 have a negative connotation.