This is a valid IP address. It is a broadcast address and your NIC will treat it as such.
If you are unfamiliar with broadcast addresses, you can read up on it. If you are familiar with them, or just lazy, I'll give you the punchline. Years ago, a guy realized that this is a valid IP address. He pinged 255.255.255.255. The entire internet responded to his ping.
The result was the entire internet coming to a halt as every computer on the connected earth responded. People were not happy. Why don't people still do this? You can. As mcSey points out, you can use this when you want "all machines on your network to hear a packet." After Mr. Sneaky briefly ground the internet to a halt, the routing protocol was updated to not relay 255.255.255.255 broadcasts outside of the network. So you can ping your homemade LAN to your heart's content, but nobody outside of that small network will hear you.
Personally, I am fascinated by the idea of pinging 255.255.255.255. I mean really, what is it like to communicate with every online computer in the world at once? Did he achieve a techology singularity? Did his ISP shit itself? Did he smile for the rest of his life knowing that he pwnt the internet?