Every domain which is registered and hosted has a lot of DNS records - some of them are created automatically when you host a domain, others can be set up manually if necessary. As an illustration, the A record of a domain name is its IP address i.e. this record reveals where the web site is situated; the MX records reveal where the e-mails are handled, while with an SRV record you can use a domain name for unconventional purposes, like a Voice-over-IP service. Being able to set up and modify certain records enables you to have different services with different providers if, for instance, your current host provides stable web hosting, but has problems with the e-mail service, or you simply prefer to get a certain service from a certain company. While you can create and edit these records freely and without any limitations as you own a given domain address, a lot of companies charge extra to give you this option.