NAPTR stands for Naming Authority Pointer.
NAPTRs are primarily used in IP telephony applications in conjunction with SRV RR records within the context of ENUM.
ENUM provides a mechanism for mapping e164-format telephone numbers into the DNS. The full mechanism is described in RFC6116, but it is basically any telephone number in the form of +A.BBBBBBBBBBB, where + is a literal "+" character, A is the NPA Country Code, and BBBBBBBBBBBB is the telephone number with all non-numerals and any leading zeros stripped out.
The process works by reversing the digits of the phone number and then putting a "." between each digit, finally (in the case of public ENUM) appending the special domain, e164.arpa.
For example, the phone number 1-(416)-535-8672 ...