IPv4 is the fourth version of IP. IP is the short name of Internet Protocol. IPv4 was introduced in 1982 by the Internet Engineering Task Force (IETF). It is a standard, which routes Internet traffic and other packet-switched networks. IPv4 has limitations of its 32-bit address space. Despite, it is the most widely used version of Internet Protocol. IPv4 provides 4.294.967.296 (232) available unique addresses.
Today, because of the growth of the IoT devices and the Internet user population, IPv4 is exhausting. In 1993 Classless Inter-Domain Routing (CIDR) was introduced, which helped a great flexibility for allocating blocks of addresses. For slowing the exhaustion, the individual Internet service providers recycling addresses as they become available.