The definition of “hosting” doesn't describe only one service, but a variety of services that offer various functions to a domain name. Having a site and emails, as an example, are two individual services despite the fact that in the general case they come together, so most of the people see them as one single service. Actually, every domain name has a couple of DNS records called A and MX, which show the server that handles each specific service - the first one is a numeric IP address, which specifies where the website for the domain name is loaded from, while the latter is an alphanumeric string, which shows the server that manages the e-mails for the domain name. As an example, an A record is 220.127.116.11 and an MX record is 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 Internet domain 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 then be sent to the correct server. The concept behind employing separate records is that the two services work with different web protocols and you can have your website hosted by one company and the e-mails by another.