The BOM marker is an order indication of bytes in a text file, for each pair of 2 bytes, in the case of Unicode-16 and for the group of 4 bytes in Unicode-32.
This marker comes exclusively at the beginning of the file.
GOOD means "Byte Order Mark", that in Portuguese would be something like "Byte sorting tag".
EDIT
There is also BOM for Unicode-8, but its use is not recommended since there is only one possible ordering for characters composed by a single byte.
EDIT Print of wikipedia, showing the markers (since it is not possible to assemble tables here in the OS)
Origin: http://en.wikipedia.org/wiki/Byte_order_mark
Byte Order Mark, byte order tag, not Binary Order Mark.
– marcus
There you go...: https://www.youtube.com/watch?v=Sv8XehRa-cg (Sorry, I couldn’t resist).
– Bacco
@Bacco Huahuhua! Good... that is, the female of BOM. (just to get in the spirit of the thing =)
– Miguel Angelo
This GOOD is most used on Windows systems, right?
– epx