UTF8 with BOM and no BOM

The UTF-8 does not require a BOM, although the Unicode standard allows the use of BOMs in UTF-8.
So UTF-8 is not included in the BOM is the standard form, in the UTF-8 file to place the BOM is mainly Microsoft's habit (by the way: the small end-order with the BOM UTF-16 called "unicode" and not detailed description, this is Microsoft's habit).
The BOM (byte order mark) is prepared for UTF-16 and UTF-32 and is used to mark the byte order (byte order). Microsoft uses the BOM in UTF-8 because it can distinguish between UTF-8 and ASCII encoding, but such files can be problematic in operating systems outside of Windows.

The difference between "utf-8" and the utf-8"with BOM is that there is no BOM. There is no U+feff at the beginning of the file.

UTF8 with BOM and no BOM