Short for byte order mark, BOM is the character code (such as U+FEFF) at the beginning of a data stream that is used to define the byte order and encoding form. BOM is most commonly associated with plaintext files where it is not known if the file is in big or little endian format. BOM is optional for Unicode text files. However it cannot be used in files containing both Unicode and binarydata.
See also big-endian.