I think (with reservations) that a trackback is when you reference another site/blog/forum...
So if say we posted a link/URL to a recipe on someone's blog...on that blog you would see that we had linked to them also...
Does that make sense?
It's like when you write an essay at college/university and you quote from someone's published book and reference them to show you didn't steal/plagerise the information...but as we're on the interweb

we have the ability (with specific software) to illustrate who has used your information...
So it tracks back and forth...if it were a recipe...the original website where the recipe was found...would show the people that had linked to it...
Ok lol I'm way tired and prolly rambling....nite