--- title: "Glossary of phone, email and IP lookup terms" url: "https://lookvalid.com/glossary.md" canonical_url: "https://lookvalid.com/glossary" last_updated: "2026-10-18" type: "index" summary: "Plain-language definitions of 39 terms used in phone, email, IP and domain validation, from HLR and LRN to DMARC, ASN and RDAP." --- # Glossary of phone, email and IP lookup terms Plain-language definitions of 39 terms used in phone, email, IP and domain validation, from HLR and LRN to DMARC, ASN and RDAP. 39 terms from phone, email, IP and domain validation, defined in plain words, with the LookValid product and docs that relate to each. ## Phone numbers - [Area code](https://lookvalid.com/glossary/area-code.md): An area code is the first three digits of a North American phone number, assigned to a geographic region such as part of a state or province. - [Carrier lookup](https://lookvalid.com/glossary/carrier-lookup.md): A carrier lookup names the telephone company that currently serves a number. - [CNAM (Caller ID Name)](https://lookvalid.com/glossary/cnam.md): CNAM is the database record that links a phone number to the name shown on the recipient's screen, usually limited to 15 characters. - [E.164](https://lookvalid.com/glossary/e164.md): E.164 is the international format for phone numbers: a plus sign, the country code, then the national number, with no spaces or punctuation and at most 15 digits. - [HLR (Home Location Register)](https://lookvalid.com/glossary/hlr.md): The Home Location Register is a database inside a mobile network that records each subscriber and which network equipment currently serves them. An HLR lookup asks that database about a mobile number. - [Line type](https://lookvalid.com/glossary/line-type.md): Line type is the kind of service a phone number belongs to: mobile, fixed line, VoIP, toll free, premium rate and so on. - [LRN (Location Routing Number)](https://lookvalid.com/glossary/lrn.md): In North America, a Location Routing Number is a ten-digit number that identifies the switch currently serving a ported phone number, so calls can be routed to it. - [NANP (North American Numbering Plan)](https://lookvalid.com/glossary/nanp.md): The North American Numbering Plan is the shared telephone numbering system for the United States, Canada and a group of Caribbean and Pacific countries and territories, all under country code +1. - [Number portability](https://lookvalid.com/glossary/number-portability.md): Number portability is the right to keep your phone number when you change provider, or move it between a mobile and a landline service. - [Reassigned number](https://lookvalid.com/glossary/reassigned-number.md): A reassigned number is a phone number that was disconnected and later given to a different person. - [SMS pumping](https://lookvalid.com/glossary/sms-pumping.md): SMS pumping is fraud in which attackers trigger large numbers of text messages, such as one-time passcodes, to phone numbers they profit from. - [Toll-free number](https://lookvalid.com/glossary/toll-free-number.md): A toll-free number is a phone number the person calling does not pay for; the receiving party does. - [VoIP number (Voice over Internet Protocol)](https://lookvalid.com/glossary/voip-number.md): A VoIP number is a phone number delivered over the internet instead of a traditional phone line or a mobile network. ## Email - [Catch-all](https://lookvalid.com/glossary/catch-all.md): A catch-all domain accepts mail sent to any address at the domain, whether or not a mailbox exists. - [Disposable email](https://lookvalid.com/glossary/disposable-email.md): A disposable email address is a temporary mailbox, created for a single sign-up and thrown away afterwards. - [DKIM (DomainKeys Identified Mail)](https://lookvalid.com/glossary/dkim.md): DKIM adds a digital signature to each email so the receiver can check that the message came from the signing domain and was not altered on the way. - [DMARC (Domain-based Message Authentication, Reporting and Conformance)](https://lookvalid.com/glossary/dmarc.md): DMARC is a DNS policy that tells receivers what to do with mail that fails SPF and DKIM checks tied to the visible "From" domain, and where to send reports. - [Hard bounce](https://lookvalid.com/glossary/hard-bounce.md): A hard bounce is a permanent delivery failure, usually because the address does not exist or the domain cannot receive mail. - [MX record (Mail Exchanger record)](https://lookvalid.com/glossary/mx-record.md): An MX record is a DNS entry that names the servers which accept email for a domain, each with a priority number. - [Role account](https://lookvalid.com/glossary/role-account.md): A role account is an email address named for a function instead of a person, such as info@, sales@ or support@. - [SMTP verification](https://lookvalid.com/glossary/smtp-verification.md): SMTP verification checks whether a mailbox exists by starting a delivery conversation with the mail server and stopping before any message is sent. - [Spam trap](https://lookvalid.com/glossary/spam-trap.md): A spam trap is an email address that exists to catch senders with poor list practices; real people never subscribe to it. - [SPF (Sender Policy Framework)](https://lookvalid.com/glossary/spf.md): SPF is a DNS record that lists which servers are allowed to send email for a domain. ## IP addresses and networks - [ASN (Autonomous System Number)](https://lookvalid.com/glossary/asn.md): An Autonomous System Number identifies a network that is run under a single routing policy, such as an internet provider, a cloud company or a large organization. - [CIDR (Classless Inter-Domain Routing)](https://lookvalid.com/glossary/cidr.md): CIDR notation writes a block of IP addresses as a starting address and a prefix length, such as 192.0.2.0/24. - [Datacenter IP](https://lookvalid.com/glossary/datacenter-ip.md): A datacenter IP address belongs to a hosting or cloud provider, so traffic from it comes from a server instead of a person at home or on a phone. - [IP geolocation](https://lookvalid.com/glossary/ip-geolocation.md): IP geolocation estimates where an internet connection is located from its IP address. - [RDAP (Registration Data Access Protocol)](https://lookvalid.com/glossary/rdap.md): RDAP is the standard way to ask who registered a domain, IP block or ASN, answered as structured JSON over HTTPS. - [Residential proxy](https://lookvalid.com/glossary/residential-proxy.md): A residential proxy routes traffic through an address that an ordinary home internet customer holds, so the traffic looks like a normal household. - [Reverse DNS (pointer (PTR) record)](https://lookvalid.com/glossary/reverse-dns.md): Reverse DNS maps an IP address back to a hostname, using a PTR record, the opposite direction of an ordinary DNS lookup. - [Tor exit node](https://lookvalid.com/glossary/tor-exit-node.md): A Tor exit node is the last relay in the Tor network, the server whose address websites see when someone browses through Tor. - [VPN (Virtual Private Network)](https://lookvalid.com/glossary/vpn.md): A VPN sends a device's traffic through an encrypted tunnel to a server run by the VPN provider, so websites see the server's address instead of the user's. ## Domains and websites - [Domain age](https://lookvalid.com/glossary/domain-age.md): Domain age is how long ago a domain name was first registered. - [Link in bio](https://lookvalid.com/glossary/link-in-bio.md): A link-in-bio page is a single web page that gathers a person's or brand's important links so they can be placed in a social profile that allows only one. - [WHOIS](https://lookvalid.com/glossary/whois.md): WHOIS is the older protocol and record format for looking up who registered a domain or IP block. ## Data and agents - [Data enrichment](https://lookvalid.com/glossary/data-enrichment.md): Data enrichment adds missing details to a record you already hold, such as finding the company for an email address or the job title for a name. - [Firmographics](https://lookvalid.com/glossary/firmographics.md): Firmographics are facts that describe a company, such as its industry, size, location and website, in the way demographics describe a person. - [MCP (Model Context Protocol)](https://lookvalid.com/glossary/mcp.md): The Model Context Protocol is an open standard that lets AI assistants and agents call outside tools and data sources through one consistent interface. - [Skip trace](https://lookvalid.com/glossary/skip-trace.md): Skip tracing is finding the current contact details of a person who is hard to reach, starting from information you already have.