Spam in blogs (also known as blog spam, comment spam, or social spam) is a form of Spamdexing. (Note that blog spam also has another meaning, specifically when a blog author creates posts without adding any informational or educational value solely for publishing them on other websites) It may be done by posting random comments on other blog websites (usually by an automated process) or by copying other websites' content and using it on free-to-use publishing services like Blogger and WordPress or publicly accessible wikis, digital guest books, and internet forums.

In such posts and comments, spammers use these methods to artificially inflate their website ranking by linking back (also referred to as backlink) to their web pages. Backlink helps search algorithms determine the popularity of a web page, which plays a major role for search engines like Google and Microsoft Bing to decide a web page ranking on a certain search query. Normally, a web page with more backlinks is considered the most valuable. This helps the spammer's website to list ahead of other sites for certain searches, which helps them to increase the number of visitors to their website.