What is a domain availability check?
A domain availability check allows you to check whether the domain name you wish to use is still available. If the domain name is still free, it can be registered with a domain registrar supplier. If the domain name is already taken, you will have to choose a different domain name and register that one.
A domain check tool looks directly in the domain services' databases to check the domain names. This means that it's okay to assume that any domain name that shows up as available actually is available for registration.