The Internet Corporation for Assigned Names and Numbers, ICANN in short, is a not for profit organization that co-ordinates the assignment of unique internet names and the IP address space. All devices connected to the internet requires an IP address and often a domain name too, enabling devices to find each other and to communicate with each other.
ICANN plans broader internet policy too as it is the organisation that decides on the rules for domain names and also how IP addresses are assigned around the world. ICANN is the organisation that decides which new generic TLDs (top level domains) are released.
ICANN’s role is to co-ordinate communication between all online internet devices, and to do this it has to co-ordinate DNS (the domain name system) as well as IP address allocation. In addition, ICANN will also assign TLDs and manages protocol identifiers and the root DNS name servers.
Back in 2009 ICANN enabled the use of IDNs (internationalized domain names) which implies that people register domain names and access domain names which are not in the Latin alphabet.
Many of the ICANN operations are managed by IANA, which was previously operated by the US government but which is now a part of ICANN.