What's so special about 0xffff EEPROM checksum

[Nerius Landys]

I'm looking at driver code in the FreeBSD kernel, and pretty much
everywhere I look I see a check for EEPROM checksum.  It's always
0xffff.  What is so special about this value 0xffff?  Is this value
agreed upon by hardware manufacturers?  So basically they have one end
slot for data where they put in the last bytes in order to ensure that
the checksum is always 0xffff?