The definition of “hosting” does not describe just one service, but a set of services that offer different functions to a domain name. Having a website and emails, for instance, are two independent services although in the general case they come together, so most of the people consider them as one single service. In fact, every single domain 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 website for the domain address is loaded from, while the second one is an alphanumeric string, which shows the server that handles the emails for the domain address. As an illustration, an A record is 126.96.36.199 and an MX record is 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 address has and the traffic/message is first directed to that company. In case you have custom records on their end, the Internet browser request or the e-mail will be forwarded to the correct server. The concept behind working with 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.