Trackback is basically a way of letting you know that some one has used your website/blog post link on there website or blog. Its auto built in wordpress blogs In terms of SEO its a back link in terms of black hat seo you can fake this
A trackback is one of three types of linkbacks, methods for Web authors to request notification when somebody links to one of their documents. This enables authors to keep track of who is linking, and so referring, to their articles. Some weblog software programs, such as Wordpress, Movable Type, Typo,Community Server and Kentico CMS, support automatic pingbacks where all the links in a published article can be pinged when the article is published. The term is used colloquially for any kind of linkback. Source: Wikipedia