public IPv4
also: public IP, global IP, external IP
A public IPv4 address is a globally routable IP address assigned by IANA and ISPs that allows a device to communicate directly with other devices across the internet.
A public IPv4 address is a unique, globally-routable internet address that identifies a device on the public internet. Unlike private IP addresses (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), public IPs are not reserved and can be reached from any other device on the internet.
Public IPv4 addresses are allocated by IANA (Internet Assigned Numbers Authority) to Regional Internet Registries, which then distribute them to ISPs and organizations. For example, if your home router has the public IP 203.0.113.45, remote servers can initiate connections to your network using that address.
In modern deployments, public IPv4 addresses are increasingly scarce and expensive due to the limited 4.3 billion possible addresses (IPv4 has 32-bit addressing). Many organizations now use NAT (Network Address Translation) to share a few public IPs among many private internal devices, or migrate to IPv6 for expanded address space.