What is a Whois Search?

A Whois Search (contraction of "who is?") is a tool that allows you to consult Registries’ databases in order to obtain information on a domain name status and availability: whether it is already registered or not.    
Moreover, with this service you can extract details about the owner of a domain name, their address, their e-mail and even their telephone number. It is very useful when it comes to checking the trustworthiness of certain websites.