The word “hosting” does not describe a particular service, but a variety of services which provide a variety of functions to a domain name. Having a site and emails, as an illustration, are two separate services despite the fact that in the general case they come together, so most people think of 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 deals with each particular service - the former is a numeric IP address, which defines where the website for the domain name is loaded from, while the latter is an alphanumeric string, which shows the server that handles the e-mails for the domain. For instance, an A record would be 220.127.116.11 and an MX record would be mx1.domain.com. Each time you open a website or send an e-mail, 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 Internet browser request or the e-mail will then be forwarded to the correct server. The concept behind working with separate records is that the two services employ different web protocols and you could have your site hosted by one service provider and the emails by another.