a dynamic IP address is an IP address that is rotated or changed regularly.

A dynamic IP address is an IP address assigned by a DHCP server (or ISP), that is rotated or changed regularly.

Dynamic IPs are often used by ISPs, in order to save on the number IPs in use. They also are often used by routers in LAN setups. A DHCP server is used to automatically configure any newly connected device with an IP address.