The word “hosting” does not describe a particular service, but a variety of services that offer a variety of functions to a domain address. Having a website and e-mails, as an illustration, are two individual services although in the general case they come together, so a lot of people see them as one single service. In fact, every 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 specifies where the website 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. As an illustration, 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 address has and the traffic/message is first directed to that company. If you have custom records on their end, the browser request or the email will be forwarded to the correct server. The reasoning behind using separate records is that the two services employ different web protocols and you could have your website hosted by one company and the emails by another.