Unique identifier in the context of Name service

A serial number (SN) is a unique identifier used to uniquely identify an item, and is usually assigned incrementally or sequentially.

Despite being called serial "numbers", they do not need to be strictly numerical and may contain letters and other typographical symbols, or may consist entirely of a character string.

A geocode is a code that represents a geographic entity (location or object). It is a unique identifier of the entity, to distinguish it from others in a finite set of geographic entities. In general the geocode is a human-readable and short identifier.

Typical geocodes (in bold) and entities represented by it:

A network address is an identifier for a node or host on a telecommunications network. Network addresses are designed to be unique identifiers across the network, although some networks allow for local, private addresses, or locally administered addresses that may not be unique. Special network addresses are allocated as broadcast or multicast addresses. These too are not unique.

In some cases, network hosts may have more than one network address. For example, each network interface controller may be uniquely identified. Further, because protocols are frequently layered, more than one protocol's network address can occur in any particular network interface or node and more than one type of network address may be used in any one network.

Nominal numbers are numerals used as labels to identify items uniquely. Importantly, the actual values of the numbers which these numerals represent are less relevant, as they do not indicate quantity, rank, or any other measurement.

Labelling a pair of referees as referees "1" and "2" is a use of nominal numbers. Any set of numbers (a subset of the natural numbers) will be consistent labels as long as a distinct number is uniquely used for each distinct term which needs to be labelled. Nonetheless, sequences of integers may naturally be used as the simplest way to begin labelling; for example, 1, 2, 3, and so on.

Goods wagons or freight wagons (North America: freight cars), also known as goods carriages, goods trucks, freight carriages or freight trucks, are unpowered railway vehicles that are used for the transportation of cargo. A variety of wagon types are in use to handle different types of goods, but all goods wagons in a regional network typically have standardized couplers and other fittings, such as hoses for air brakes, allowing different wagon types to be assembled into trains. For tracking and identification purposes, goods wagons are generally assigned a unique identifier, typically a UIC wagon number, or in North America, a company reporting mark plus a company specific serial number.

A CAS Registry Number (also referred to as CAS RN or informally CAS Number) is a unique identification number, assigned by the Chemical Abstracts Service (CAS) in the US to every chemical substance described in the open scientific literature, in order to index the substance in the CAS Registry. This registry includes all substances described since 1957, plus some substances from as far back as the early 1800s. It is a chemical database that includes organic and inorganic compounds, minerals, isotopes, alloys, mixtures, and nonstructurable materials (UVCBs - substances of unknown or variable composition, complex reaction products, or biological origin). CAS RNs are generally serial numbers (with a check digit), so they do not contain any information about the structures themselves the way SMILES and InChI strings do.

The CAS Registry is an authoritative collection of disclosed chemical substance information. It identifies more than 204 million unique organic and inorganic substances and 69 million protein and DNA sequences, plus additional information about each substance. It is updated with around 15,000 additional new substances daily. A collection of almost 500 thousand CAS registry numbers is made available under a CC BY-NC license at ACS Commons Chemistry.

A vehicle registration plate, also known as a number plate (British, Indian, Pakistani English and Australian English), license plate (American English) or licence plate (Canadian English), is a metal or plastic plate attached to a motor vehicle or trailer for official identification purposes. All countries require registration plates for commercial road vehicles such as cars, trucks, and motorcycles, for hire. Whether they are required for other vehicles, such as bicycles, boats, or tractors, may vary by jurisdiction. The registration identifier is a numeric or alphanumeric ID that uniquely identifies the vehicle or vehicle owner within the issuing region's vehicle register. In some countries, the identifier is unique within the entire country, while in others it is unique within a state or province. Whether the identifier is associated with a vehicle or a person also varies by issuing agency. There are also electronic license plates.

Aadhaar (Hindi: आधार, lit. 'base, foundation, root, ground') is a twelve-digit unique identity number that can be obtained voluntarily by all residents of India based on their biometrics and demographic data. The data is collected by the Unique Identification Authority of India (UIDAI), a statutory authority established in January 2016 by the Government of India, under the jurisdiction of the Ministry of Electronics and Information Technology, following the provisions of the Aadhaar Act, 2016.

The Aadhaar identity card is also known as an "Aadhaar UID Card" or a "UID card".

In the relational model of databases, a primary key is a designated set of attributes (column(s)) that can reliably identify and distinguish between each individual record in a table. The database creator can choose an existing unique attribute or combination of attributes from the table (a natural key) to act as its primary key, or create a new attribute containing a unique ID that exists solely for this purpose (a surrogate key).

Examples of natural keys that could be suitable primary keys include data that is already by definition unique to all items in the table such as a national identification number attribute for person records, or the combination of a very precise timestamp attribute with a very precise location attribute for event records.

A national identification number or national identity number is used by the governments of many countries as a means of uniquely identifying their citizens or residents for the purposes of work, taxation, government benefits, health care, banking and other governmentally-related functions. They allow authorities to use a unique identifier which can be linked to a database, reducing the risk of misidentification of a person. They are often stated on national identity documents of citizens.

The ways in which such a system is implemented vary among countries, but in most cases citizens are issued an identification number upon reaching legal age, or when they are born. Non-citizens may be issued such numbers when they enter the country, or when granted a temporary or permanent residence permit.

A MAC address (medium access control address or media access control address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking technologies, including Ethernet, Wi-Fi, and Bluetooth. Within the Open Systems Interconnection (OSI) network model, MAC addresses are used in the medium access control protocol sublayer of the data link layer. As typically represented, MAC addresses are recognizable as six groups of two hexadecimal digits, separated by hyphens, colons, or without a separator.

MAC addresses are primarily assigned by device manufacturers, and are therefore often referred to as the burned-in address, or as an Ethernet hardware address, hardware address, or physical address. Each address can be stored in the interface hardware, such as its read-only memory, or by a firmware mechanism. Many network interfaces, however, support changing their MAC addresses. The address typically includes a manufacturer's organizationally unique identifier (OUI). MAC addresses are formed according to the principles of two numbering spaces based on extended unique identifiers (EUIs) managed by the Institute of Electrical and Electronics Engineers (IEEE): EUI-48—which replaces the obsolete term MAC-48—and EUI-64.