What is dynamic IP?
Dynamic IP address is a dynamically assigned network number to a network device by a service provider through a DHCP (Dynamic Host Configuration Protocol).
Most of the ISPs (Internet Service Providers) use DHCP to assign IP address to their clients devices dynamically. The reason is that IPv4 protocol has a limited address space, and usually number of free IP address in a providers network are also limited. While not all the clients of ISP are connected to the Internet at the same time, it is reasonable to assign dynamically one of free IP-addresses in the provider's address pool to newly connected client. As far, as it makes possible to reuse and assign the same address to another client after the first one is disconnected (finished to use the Internet).
DHCP protocol makes possible to do it without the need to configure a client's PC (or another device) all the time. So in most cases when you use the Internet, you have a dynamic IP. If you'll check the history of your IPs at our main page, and you'll see that the same PC has a different IP through the time (even if your PC is always connected to the Internet with the same provider), it means that your IP address is a subject to dynamic assignment by your Internet provider.