SRV, which is an abbreviation for Service, is a DNS record, which enables you to use a domain for a certain service different from a website. By creating a few SRV records, you can use the domain address with different companies and forward it to several servers simultaneously, each and every server handling a different service. You can specify the port number for the connection to each machine, so there won't be any interference. You can also set individual priorities and weight for two records which are used for the very same service, but forward to different servers for redundancy or load balancing. By having an SRV record you can use your domain address or a subdomain under it for a Voice-Over-IP server, for instance, and have the specific software running on several machines with different providers. Which one a client of yours will use will depend on the priority and weight values that you have set.