The term “hosting” does not describe a single service, but a number of services which offer various functions to a domain name. Having a website and e-mails, for instance, are two individual services though in the general case they come together, so a lot of people consider them as one single service. In fact, every domain has a number of DNS records called A and MX, which show the server that manages each specific service - the first one is a numeric IP address, which 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 e-mails for the domain name. As an example, an A record can be 126.96.36.199 and an MX record is mx1.domain.com. Every time you open a website or send an e-mail, the global DNS servers are contacted to check the name servers that a domain name has and the traffic/message is first forwarded to that company. In case you have custom records on their end, the web browser request or the email will be directed to the correct server. The reasoning behind using separate records is that the two services use different web protocols and you can have your website hosted by one service provider and the e-mails by another.