The definition of “hosting” does not describe just one service, but a set of services which provide a variety of functions to a domain name. Having a site and emails, for instance, are two independent services although in the general case they come together, so many people consider them as one single service. In fact, every domain has a several DNS records called A and MX, which show the server that handles each specific service - the former is a numeric IP address, which defines where the site for the domain is loaded from, while the second one is an alphanumeric string, which shows the server that manages the e-mails for the domain. For example, an A record is 22.214.171.124 and an MX record would be mx1.domain.com. Whenever you open a website 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 forwarded to that company. In case you have custom records on their end, the Internet browser request or the email will be forwarded to the correct server. The reasoning behind employing separate records is that the two services work with different web protocols and you could have your site hosted by one company and the e-mail messages by another.