Install multiple WordPress installations to single domain
Create multiple sites by using the multisite feature
As of WordPress 3.0 (released June 17, 2010), you now have the ability to create a network of sites by using the multisite feature. Prior versions of a single WordPress install were not capable of running multiple blogs. There was a version especially made for this, called WordPress MU, but it was more advanced than WordPress, and was intended for very large sites with lots of blogs, not just a few.
Installs of the WordPress 3.x branch and above now come with the native ability to create multiple blogs, referred to as a network of sites. This is because the codebase for WordPressMU was merged into core.
To enable the multisite feature, simply define multisite in the wp-config.php file by adding the following code snippet:
Compared with a typical single WordPress installation, a network installation has additional considerations. You must decide if you want to use sub-domains or sub-folders and how you want to manage them. Installing themes and plugins is different: for example, each individual site of a network can activate both, but install neither. One of the basic advantages is that you won’t have to install the same plugins over and over again as you start new sites. You also won’t have to upgrade multiple WordPress installations whenever a new version is released – a single click of the button will get all your sites completely up to date.