Akismet is a spam buster project owned by WordPress.com. To activate Akismet you should have WP-API-Key by first creating an account in WordPress.com. After obtaining API Key, login to your WP-Admin page and activate Akismet. Enter your WP-API-Key whenever asked.
If you blog at wordpress.com, then Akismet is already available, you don’t have to enter WP-API-Key since WordPress.com do it automatically.
Here’s what Wikipedia said:
Akismet, or Automattic Kismet, is a spam filtering service created by Automattic and released on October 25, 2005, the corporation which employs most of the main developers of the weblog platform WordPress. Akismet attempts to filter link spam from blog comments and spam TrackBack pings. The filter works by combining information about spam captured on all participating blogs, and then using those spam rules to block future spam. Akismet has captured one billion spam comments and pings as of March 2007.
Akismet can be used not only on WordPress, but also Bloggers with a Yahoo! hosting account.
