A backlink is a link on someone else’s website that points to yours — it “comes back” to you from outside. If a newspaper writes about a shop and puts the shop’s web address in blue, that is a backlink to the shop. People who look after websites care about backlinks because search engines treat a good one as a kind of vote: this page was worth pointing to. Many honest backlinks from trusted sites can help a page show up higher; a pile of junk ones can do the opposite. The word lives in internet and marketing talk. You can use it as a verb: to backlink to a page. The “back” is the direction — toward you, from another site — not “back” as in the body, and not “the old link.” A link you place on your own page that goes out is just a link, not a backlink.