Trackbacks in Wordpress

99.99% of them will be spam these days. There are even automated tools to help someone spam in this fashion. I highly recommend that you disable this feature in WordPress and delete any existing ones (other than ones from online friends who you know aren't trying to spam you).

Whenever someone links to a post on your block, it sends a trackback to your blog. This feature allows people to see other posts that are related to the content on your blog. In theory, it's supposed to help your visitors get more value. In practice, there are so many blogs that do it just to get a backlink, and end up sending a bunch of spam trackbacks.

So, I usually end up denying them all. I have let a FEW trough that have been of good quality, where it was evident that it wasn't some sort of spam technique.

A lot of blogging software/platforms send out a sort of "ping" to any site/page to which a link is generated, which ultimately comes through as a "trackback". I don't really know what the point is. I know a lot of spammers use it as a means of acquiring backlinks, but I suspect most of the time the links come out as "nofollow", anyway.

You can approve them if you want. They may make your blog appear more popular/active/authoritative to your readers, I guess, for those who know what a trackback is, and aren't aware that they're often just a means for spammers to acquire a backlink. I tend to disable them (along with regular comments) on most of my sites, and for sites on which I have commenting enabled, I'll often "mark as spam" or otherwise delete those trackbacks which have clearly come from a crappy site, where the owner has only linked out for the sake of trying to acquire a backlink themselves.

So it can be a good thing for you to receive notification of a trackback, if the link you've received is on a high-traffic page, or if they're not nofollowed. But most of the time, it means or counts for absolutely jack-squat.

Introduction to Blogging « WordPress Codex

it is well-documented at the link above!