Each and every domain name that's registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be set up manually if necessary. As an illustration, the A record of a domain address is its IP address i.e. this record reveals where the website is located; the MX records reveal where the emails are stored, while with an SRV record you can use a domain address for unconventional purposes, like a Voice-over-IP service. The ability to create and modify certain records allows you to have different services with different providers if, for example, your current host provides stable web hosting, but has troubles with the e-mail service, or you simply prefer to get a specific service from a particular company. While you can set up and modify these records freely and without any limitations as you own a given domain, many companies charge extra to give you this option.