BOM

1. Short for Byte Order Mark, BOM is another name for the Unicode character at the beginning of a file that indicates whether or not a file is UTF-16 or UTF-32. 
2. Short for Bill of Materials, BOM is a complete listing of everything that makes up a product. For example, a computer purchased from a computer manufacturer will have a BOM of every part and/or a purchasable parts. A BOM contains the name of the part, it's part number, and the quantity of each parts.
3. Short for Beginning of Medium, BOM is a string of characters that mark the beginning of a medium such as a tape drive.
4. Short for Beginning of Message, BOM is a signal or string of characters that indicate a message is starting.

Also see: EOF, Programming definitions, Tape drive definitions, Unicode, UTF