BOM (byte order mark)
It is not a character, but a byte sequence at the beginning of the file.
It can be found at the start of a text file and indicates
- The byte order, or endianness, of the text file
- The fact that the text stream's encoding is Unicode, to a high level of confidence;
- Which Unicode encoding the text stream is encoded as.
If you pass a character set to a file reader, you don't need to handle the BOM.