Irrelevant comments posted to a blog for the sole purpose of dropping a link to the spammer’s website
Comment spam is also called a spomment, a portmanteau of the words ‘spam’ and ‘comment’. These are typically characterized by the presence of replies that are irrelevant to the blog entry, along with a link that leads to the commenter’s website.
The use of comment spam is considered a “Black Hat” SEO technique, which is used to try and improve a site’s link popularity and anchor text.
However, there are many ways for webmasters to combat blog spam, such as blog site plugins (e.g. Akismet, Challenge, Referrer Bouncer) that block most types of spam comments.
The search engines also have a ‘nofollow’ initiative that lets webmasters tell search engine robots not to give credit to links in blog comments. However, this only prevents comments if spambots are setup to ignore “nofollow blogs” and many of spamming scripts are not very refined. Although in the long run it could lead to less spam comments if it makes the technique less effective on a global scale.
How to Stop Comment Spam
SitePoint (March 31, 2005)