You can read any of the following links or articles to get a general understanding of a trackback or backlink. In short, they display other blogs or websites that "link" "back" to your post(s).  This, generally is a good thing.
Typepad (from the Typepad Support pages):
• What is a trackback:
• Sending a trackback:
• Acccepting a trackback:

Blogger (from Blogger Help pages):
• What are backlinks and how to use them:

WordPress (from FAQ pages and Forum find):
• How to send a Trackback:
• What is a trackback:
• Adding a trackback:
• Overall search on "trackback" and all the results:

Hope this helps!

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