The definition of “hosting” doesn't describe one service, but a number of services which offer numerous functions to a domain address. Having a website and e-mails, as an example, are two individual services although in the general case they come together, so most people consider them as one single service. In fact, each and every domain name has a several DNS records called A and MX, which show the server that deals with each specific service - the first one is a numeric IP address, that defines where the website for the domain address is loaded from, while the latter is an alphanumeric string, which shows the server that deals with the e-mails for the domain address. For instance, an A record would be 220.127.116.11 and an MX record is mx1.domain.com. Each time you open a website 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 forwarded to that company. If you have custom records on their end, the Internet browser request or the email will then be forwarded to the correct server. The concept behind working with separate records is that the two services work with different web protocols and you could have your site hosted by one provider and the e-mail messages by another.