What's a Trackback??

Hmm, well I've read and seen countless trackbacks while surfing the net. But I always wondered how websites 'knew' that the trackbacks existed. I guess from the little bit I read, if you use a particular link to an article (called a trackback link) then the site to which you link will recognize your blog. I suppose if I just linked to the article without using the special trackback link then it wouldn't appear? I'm not certain. This shouldn't be confusing, but maybe I get a pass because I haven't done it before? In any event, I'm going to try linking below and see what happens. Whoopee!