Akismet is a spam solution service which is different from others plugins. It is used to determine whether contents of the comments is spam or not and stop the spam content of the comment to be displayed on the blog. Akismet can be used with wordpress 2.0 or higher version of it.
One need to download, install and activate the Akismet plugins for their domain. To activate the Akismet plugins one need API Key for their wordpress blog. Once the API Key is applied in Akismet configuration section under plugins Akismet will be activated.