Acronym for Trivial File Transfer Protocol.
So named because it does nothing but transfer files. There are no configurable ports (it always runs on port 69), no passive transfers, nothing.
You install a TFTP server and point it at a directory. Then, you give your client an IP address, you point it at the IP address of a TFTP server, and say 'get filename'. If that filename is in the directory, the TFTP server will send it to the client.
Note from WilliamLangford?.
We started experimenting with using PXE DHCP TFTP booting a DOS Ghost image to ease the duplication of servers we send to the field. Our DHCP server is the same as our TFTP server, running under Slackware version 10.x. pxelinux.0 was refusing to find any information setup in the DHCPD or TFTP config files until we added the "next-server same.server.ip.address;" to the subnet definition we were attempting to PXE boot in dhcpd.conf. Apparently pxelinux.0 wanted that information to know what to connect to for TFTP booting.