The "Internet Protocol" (IP) address is like a phone number for every device on the internet.
The addressing system in IPv4 was made up of four 8-bit (0-255) numbers, so an IPv4 address looks like something like 192.168.1.1.
In the mid-90's work began on IPv6, which expands the address format from a 32-bit number to a 128-bit number - allowing nearly as many potential addresses as there are atoms on the earth.
Most consumer equipment is still using iPv4, but most behind the scenes networking is IPv6. Most humans don't need to worry about it.