One is related to serial programming. Serial programming and data downloading is enabled. If you want to enable the Brown-Out Detector circuit.
Television And Radio Announcing Pdf Writer on this page. The fuse entry is present to indicate to the user that a fuse exists on the ATmega1281 called SPIEN, and the description explains that the fuse is used to determine whether the chip will allow you to program it through its ISP interface or not. The question mark is displayed because the programming dialog box is setup to communicate using the ISP protocol, and it isn't possible to inspect/modify the state of the SPIEN fuse using the ISP interface. If you switched to an alternative programming interface (eg. High voltage parallel or JTAG programming) then the SPIEN fuse would become accessible/modifiable. 'SPI programming' is somewhat of an unfortunate name for the process, because it doesn't actually use the onboard SPI port of an ATmega1281; rather, it uses pins that are known as PDI (programming data in) and PDO (programming data out).
