SRV is one of the DNS record types (like A, CNAME, and MX).
Most DNS record types provide information about one particular type of service or protocol. For example, the MX record specifies the IP address of the server that handles email for a domain.
The SRV record is an open-ended record — it can be used to specify any type of service (including ones not invented yet). This gives the DNS record system flexibility, instead of having to create a new record standard for each new protocol that is invented and used.
SRV records are commonly used for identifying a number of different protocols. Most interestingly (we think) is Minecraft servers.
