All domains have an Auth Code - effectively a randomly generated password unique to them. The main purpose of an Auth Code is to authorise the transfer of a domain from one registrar to another. A Auth Code is generated on request and can be requested at any time.
Note that sometimes Auth Code can also be referred to as an EPP Code in some situations.
Having a valid Auth Code gives a person virtually complete control over the domain name. Keep this in mind before passing the Auth Code onto anyone else as they can potentially take over complete ownership of your domain.
Registrars are required to provide your Auth Code upon request. SiteHost does not store the Auth Code for your domain, but provides a method for you to request a new Auth Code which will be generated and sent to the domain registrant email address.