I should have posted sooner. There's no such thing as 'wildcard domains' with the exception of SSL certificates. However, as related to DNS and a web server it cannot exist.

Wildcard subdomains are another matter.

Essentially, when a surfer wants to go to a site they enter the domain.tld (tld stands for top level domain, ie. .com and .net). As sites expand they may want to have parts of the site hosted on other servers or using other accounts so they create a subdomain, such as sub.domain.tld. A wildcard subdomain is when DNS zone record for the domain has an entry similar to:
*.domain.tld. IN A XXXX 123.123.12.123

This is going to forward any request for a subdomain of that domain to the IP address 123.123.12.123.

The httpd server will have an entry for domain.tld with an alias entry of *.domain.tld. So all subdomains will be forwarded to the same site (file folder on the server) as the domain.

It's useful when you want to use mod_rewrite to direct different subdomains to other folders or files.