The term “hosting” does not describe a particular service, but a variety of services which provide various functions to a domain address. Having a site and e-mails, as an illustration, are two independent services even though in the general case they come together, so many people think of them as one single service. In fact, each domain name has a number of DNS records called A and MX, which show the server that deals with each specific service - the former is a numeric IP address, which specifies 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 example, an A record can be 123.123.123.123 and an MX record is mx1.domain.com. Whenever you open a site or send an e-mail, the global DNS servers are contacted to check the name servers that a Internet domain has and the traffic/message is first directed to that company. If you have custom records on their end, the browser request or the e-mail will be forwarded to the correct server. The concept behind using separate records is that the two services employ different web protocols and you can have your site hosted by one provider and the emails by another.