Canonical tags help tell search engines how to avoid duplicate content on your site. See http://www.canonicaltag.com/ to learn about canonical tags.

WSN uses canonical tags by default. If you wish to turn them off you can do so at Admin Panel -> Settings -> SEO -> "Use Canonical Tags?". Below that there's an additional checkbox option asking if you'd like to have aliased listings and categories point to the original submission in the canonical tag. If you check this box (which is not checked by default) your aliases will no longer appear in search engine indexes. Whether this is desirable or undesirable is a up to you or your SEO consultant to decide.