Wildcard subdomain facility is a function that allows you to use scripts, such as PHP scripts, to generate subdomains on the fly and point it to any preset content or queried information.

Traditionally, if you don't have wildcard subdomain facility on your server, your folders and subdomain are created manually. If you use scripts and have wildcard facility enabled, you can create subdomain.yourdomain.com automatically with any keyword you choose.

A wildcard subdomain is a method for matching requests for a non-existent subdomain i.e. subdomains for which there is no record for. With wildcard subdomains enabled, if a visitor types in someplace.yourdomain.com, you can make the domain resolve to a default "landing" page, or you can query a database and find out what the content for this subdomain should be.

You would most likely see this feature on a blog, where categories of the blog are the subdomains, such as cooking.yourblog.com.

Most webhosting providers do not support wildcard facilities and scripts that generate them as it takes alot of server resources and is greatly abused.

Softwares like WordPress MU (multiuser) can create subfolders automatically via scripts and need wildcard subdomain facility to use the option. Most webhost do not allow the use of WordPress MU on their server.

If your webhost supports wildcard subdomains, then all you have to do is create a subdomain and name it " * ". Point the subdomain to your public_html. This sets up wildcard dns. From there the .htaccess file that WordPress MU uses to rewrite subdomains.

Two hosting companies that do support wildcard subdomain facility include HostGator and JustHost.