The word “hosting” doesn't describe one service, but a variety of services which provide different functions to a domain address. Having a website and emails, for example, are two individual services even though in the general case they come together, so a lot of people think of them as one single service. In fact, each and every 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 latter is an alphanumeric string, which shows the server that handles the emails for the domain name. As an example, an A record can be 184.108.40.206 and an MX record would 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 forwarded to that company. In case you have custom records on their end, the browser request or the email will then be directed to the correct server. The concept behind using separate records is that the two services employ different web protocols and you can have your website hosted by one company and the e-mails by another.