DHCP discovery is the everyday user of 255.255.255.255 — a device with no IP yet broadcasts "is there a DHCP server?" to it. You will also see it as the default subnet mask value for a single host (/32), which is a different use of the same four octets.
Notable IP addresses / 255.255.255.255
255.255.255.255
255.255.255.255 — limited broadcast
Broadcast address (RFC 919)Not owned — reserved
The limited broadcast address: a packet sent here is delivered to every host on the local network segment and is never forwarded by routers.
Related addresses
Frequently asked questions
Why does my subnet mask show 255.255.255.255?
That is a /32 mask, meaning the address is a single host with no on-link neighbours. It is normal for VPN tunnel interfaces and some cellular connections.