The term “hosting” does not describe only one service, but a set of services which offer various functions to a domain. Having a site and emails, for instance, are two separate services even though in the general case they come together, so a lot of people see them as one single service. In reality, every domain name has a number of DNS records called A and MX, which show the server that handles each specific service - the former is a numeric IP address, which identifies where the site for the domain is loaded from, while the second one is an alphanumeric string, which shows the server that deals with the emails for the domain. As an illustration, an A record would be 126.96.36.199 and an MX record is mx1.domain.com. Every time you open a site or send an email, the global DNS servers are contacted to check the name servers that a Internet domain has and the traffic/message is first forwarded to that company. In case you have custom records on their end, the Internet browser request or the e-mail will then be forwarded to the correct server. The idea behind employing separate records is that the two services use different web protocols and you could have your site hosted by one company and the emails by another.