The UCS-2 and UTF-16 encodings specify the <answer>Unicode Byte Order Mark</answer> (BOM) for use at the beginnings of text files, which may be used for byte ordering detection (or byte endianness detection). The BOM, code point U+FEFF has the important property of unambiguity on byte reorder, regardless of the Unicode encoding used; U+FFFE (the result of byte-swapping U+FEFF) does not equate to a legal character, and U+FEFF in other places, other than the beginning of text, conveys the zero-width non-break space (a character with no appearance and no effect other than preventing the formation of ligatures).
What does BOM stand for? 
Unicode Byte Order Mark