When your computer connects to the network, it asks for it's address on the network. As it does not know where to ask, it sends a broadcast message to all computers on the same network (address 255.255.255.255). The service it wants to read is the DHCP service located on the servers' port 67, therefore the :67 after the address.

The address it gets in return is always only temporary. The server admin can define how long such lease lasts, and when a computer calls the DHCP again later (before the lease runs out) it gets the same address, and the lease timer starts again.

Some networks with high turnover (guest networks in a cafe, or similar) have rather fast lease expiries, therefor leading to regular requests.