The word “hosting” does not describe only one service, but a set of services that offer a variety of functions to a domain address. Having a site and emails, as an illustration, are two separate services even though in the general case they come together, so many people consider them as one single service. Actually, every single domain name has a couple of DNS records called A and MX, which show the server that manages each particular service - the first one is a numeric IP address, that defines where the site for the domain name is loaded from, while the second one is an alphanumeric string, which shows the server that deals with the e-mails for the domain address. For instance, an A record would be 123.123.123.123 and an MX record can be mx1.domain.com. Each time you open a site or send an email, the global DNS servers are contacted to check the name servers that a domain has and the traffic/message is first directed to that company. In case you have custom records on their end, the web browser request or the email will then be directed to the correct server. The reasoning behind employing separate records is that the two services use different web protocols and you can have your site hosted by one company and the emails by another.