DHCID : DHCP identifier (RFC 4701)
Used in conjunction with the FQDN option to DHCP

NS : name server record (RFC 1035)
Delegates a DNS zone to use the given authoritative name servers

NAPTR : Naming Authority Pointer (RFC 3403)
Allows regular expression based rewriting of domain names which can then be used as URIs, further domain names to lookups, etc.

SOA : start of authority record (RFC 1035)
Specifies authoritative information about a DNS zone, including the primary name server, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone.

CNAME : Canonical name record (RFC 1035)
Alias of one name to another: the DNS lookup will continue by retrying the lookup with the new name.

NSEC3PARAM : NSEC3 parameters (RFC 5155)
Parameter record for use with NSEC3

OPT : Option (RFC 2671)
This is a 'pseudo DNS record type' needed to support EDNS

SIG : Signature (RFC 2535)
Signature record used in SIG(0) (RFC 2931). Until RFC 3755 was published, the SIG record was part of DNSSEC; now RRSIG is used for that.

AXFR : Full Zone Transfer (RFC 1035)
Transfer entire zone file from the master name server to secondary name servers.

SSHFP : SSH Public Key Fingerprint (RFC 4255)
Resource record for publishing SSH public host key fingerprints in the DNS System, in order to aid in verifying the authenticity of the host.

DNAME : delegation name (RFC 2672)
DNAME will delegate an entire portion of the DNS tree under a new name. In contrast, the CNAME record creates an alias of a single name. Like the CNAME record, the DNS lookup will continue by retrying the lookup with the new name.

MX : mail exchange record (RFC 1035)
Maps a domain name to a list of mail exchange servers for that domain

IXFR : Incremental Zone Transfer (RFC 1995)
Requests a zone transfer of the given zone but only differences from a previous serial number. This request may be ignored and a full (AXFR) sent in response if the authoritative server is unable to fulfill the request due to configuration or lack of required deltas.

IPSECKEY : IPSEC Key (RFC 4025)
Key record that can be used with IPSEC

A : address record (RFC 1035)
Returns a 32-bit IPv4 address, most commonly used to map hostnames to an IP address of the host, but also used for DNSBLs, storing subnet masks in RFC 1101, etc.

NSEC : Next-Secure record (RFC 4034)
Part of DNSSEC—used to prove a name does not exist. Uses the same format as the (obsolete) NXT record.

AFSDB : AFS database record (RFC 1183)
Location of database servers of an AFS cell. This record is commonly used by AFS clients to contact AFS cells outside their local domain. A subtype of this record is used by the obsolete DCE/DFS file system.

TSIG : Transaction Signature (RFC 2845)
Record that supports one set of security mechanisms for DNS. Used to secure communication between DNS resolvers and Name servers, in contrast to DNSSEC, which secures the actual DNS records from the authoritative name server.