Network and addresses
IPv4 address
The server's public address like 203.0.113.10. Usually one is included in the plan.
IPv4 is the address by which a server is visible on the internet. IPv4 addresses are scarce worldwide, so they cost money: usually one is included in the plan and extra ones are billed monthly.
If a VPS has no IPv4 of its own (only IPv6 or a shared address), some visitors and services will not reach it — worth checking on the cheapest plans.