In torrent what is seed, feed & peer?
A seed is someone who has 100% of the file and is uploading it.
A leech is someone who is downloading the file. This implies that they aren't uploading any parts of the file at all. This might be because they don't have any complete parts of the file or have turned off uploading. However, most torrent clients won't allow, or seriously throttle, requests from someone not giving back to the torrent so pure leechers are going to be few and far between.
A peer is someone who is both downloading and uploading the file - and by definition has less than 100% of the file. A strict definition would include seeds in the peers as they are sharing the file, but using peer just for someone with less than 100% is common (µTorrent for example makes this distinction in its UI).
A feed is the actual torrent file itself, although this is a less common usage of the term.
A torrent with no seeds is more likely to be incomplete, though there may be 100% of the file distributed amongst the other peers.
Seeds are the people uploading the file so you, and others (called leechers) can download it. Peers are the people you are sharing the file with, so Leechers and Seeders together.