BOOTP stands for Boot Protocol and is defined by RFC 951 and RFC 1542. BOOTP (Boot Protocol) may be used to boot remote computers over a network so they can get their IP address automatically and the network location of an operating system boot image.
BOOTP allows remote workstations to get an IP address prior to loading an operating system and allows diskless workstations to operate by loading their operating system over a network. BOOTP messages are encapsulated inside UDP messages and therefore its requests and replies are forwarded by routers. See How to boot a remote computer for an article about how to remote boot a diskless computer with the Linux operating system.