A PTR record associates an IP address with a canonical name. PTR records should point to a name that can be resolved back to the IP address. The name of the pointer record is not the IP address itself, but is the four IP octets of the address in reverse order followed by IN-ADDR.ARPA.
A PTR record is what lets someone do a "reverse" DNS lookup - that is, they have your IP address and want to know what your host/domain is.
VIRTBIZ colocation and dedicated server customers may have customized PTR records for the IP addresses assigned to them.