The definition of “hosting” does not describe a single service, but a set of services that provide numerous functions to a domain name. Having a site and emails, as an example, are two individual services although in the general case they come together, so many people consider them as one single service. In reality, every single domain name has a couple of DNS records called A and MX, which show the server that deals with each specific service - the first one is a numeric IP address, which identifies where the website for the domain is loaded from, while the latter is an alphanumeric string, which shows the server that handles the emails for the domain. For instance, an A record can be 184.108.40.206 and an MX record can be mx1.domain.com. Whenever you open a site or send an email, 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. If you have custom records on their end, the Internet browser request or the e-mail will be sent to the correct server. The idea behind working with separate records is that the two services work with different web protocols and you can have your site hosted by one provider and the e-mails by another.