Stands for "Internet Assigned Numbers Authority."
The IANA is a standards authority that operates in affiliation with ICANN. They are responsible for coordinating several globally-unique numbering systems that keep the Internet going. Its primary roles are allocating blocks of IP addresses, managing the root zone DNS entries, and maintaining a registry of standard Internet protocols.
Without a central authority charged with distributing IP addresses, computer networks wouldn't know how to route Internet traffic. However, with millions of possible IP addresses available, it's not feasible for a single entity to distribute them all individually. Instead, the IANA allocates blocks of IP addresses to Regional Internet Registries (RIRs). The RIRs then distribute addresses to National Internet Registries (NIRs) and ISPs; they, in turn, assign them to individual customers.
In addition to assigning blocks of IP addresses, the IANA is responsible for managing the upper-most parts of the DNS hierarchy, known as the root zone. It maintains a central registry of top-level domains (like ".com," ".biz," or ".uk") and delegates the administration of each one to a registrar. These registrars can then sell and assign domain names using those TLDs. For example, the ".com" TLD is delegated to Verisign for them to manage, while ".org" is delegated to the non-profit Public Interest Registry.
The IANA's third major responsibility is maintaining a registry of standard Internet protocols. HTML status codes, port numbers, language abbreviations, and MIME types are all standards that software, operating systems, and web servers need to agree on for the Internet to work. For example, the SSH protocol's use of port 22 is part of the Service Name and Transport Protocol Port Number Registry maintained by the IANA. By referencing a central database of standard protocols, software and websites can use standard protocols to work together seamlessly.