The definition of “hosting” does not describe just one service, but several services that offer numerous functions to a domain. Having a site and emails, for instance, are two independent services despite the fact that in the general case they come together, so most people think of them as one single service. Actually, each and every domain name has a couple of DNS records called A and MX, which show the server that manages each specific service - the former is a numeric IP address, which identifies where the site for the domain address is loaded from, while the latter is an alphanumeric string, which shows the server that deals with the emails for the domain address. As an illustration, an A record would be 126.96.36.199 and an MX record can be mx1.domain.com. Every time you open a site or send an e-mail, the global DNS servers are contacted to check the name servers that a domain name has and the traffic/message is first forwarded to that company. In case you have custom records on their end, the web browser request or the email will be forwarded to the correct server. The idea behind working with separate records is that the two services employ different web protocols and you can have your website hosted by one service provider and the emails by another.