The term “hosting” does not describe a particular service, but a number of services that offer a variety of functions to a domain. Having a site and emails, for instance, are two individual services though in the general case they come together, so most people consider them as one single service. In fact, every single domain name has a number of DNS records called A and MX, which show the server that manages each particular service - the former is a numeric IP address, that defines where the site for the domain address 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 example, an A record is 126.96.36.199 and an MX record would be 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 domain name has and the traffic/message is first forwarded to that company. If you have custom records on their end, the browser request or the e-mail will then be directed to the correct server. The idea behind working with separate records is that the two services use different web protocols and you may have your site hosted by one provider and the e-mails by another.