Dynamic IP

The Dynamic Host Configuration Protocol (DHCP) is a standardized network protocol used on Internet Protocol (IP) networks for dynamically distributing network configuration parameters, such as IP addresses for interfaces and services. With DHCP, computers request IP addresses and networking parameters automatically from a DHCP server, reducing the need for a network administrator or a user to configure these settings manually. Wikipedia

Most routers are set default on DHCP. How your machine is configured, you can see after a login with your user data in the web interface of your router. Here you could see all connected devices with IP. You will find detail instructions in the manual of your device.