A dynamic IP is one that is assigned automatically through a process/protocol called Dynamic Host Configuration Protocol. Most routers support this mode and can have “reservations” of certain IP addresses to specific devices.
By contrast, static IP addresses are a manually assigned/configured IP address. The difference between a static IP and a reservation is that a static IP is configured directly on the device that is going to use it. A reservation is configured on the router that the device will connect to, and then that device will obtain that IP via DHCP.
In relation to Metronet’s static IP assignments, these must be manually configured, usually on the router or firewall attached directly to the ONT.