The definition of “hosting” doesn't describe a particular service, but a number of services which offer different functions to a domain address. Having a website and emails, for instance, are two separate services although in the general case they come together, so most of the people see them as one single service. In fact, each and every domain has a couple of DNS records called A and MX, which show the server that handles each specific service - the former is a numeric IP address, that 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 e-mails for the domain name. As an illustration, an A record would be 126.96.36.199 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 domain address has and the traffic/message is first directed to that company. If 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 employ different web protocols and you can have your website hosted by one provider and the emails by another.