Whois is a protocol that is access to registering information. You can reach when the website was registered, when it will be expire, what is contact details of the site with the following informations. In a nutshell, it includes these informations;
The registar is the authority where is registered. Server location specifies where it is physically. The IP of a server identifies it. It can be unique or shared between multiple sites. The next date will expire. The owner usually renews every year its domain, but some prefer buying more than a year only. Domain age is a measure of how much a site is old. Older sites have normally more importance and are more trustworthy than young ones. The date was registered for the first time.