I have been given somd source code of a program and I am trying to understand how the program works

I have got a stucture defined as

typedef struct
{
BYTE Material: 4;
BYTE : 6;
}TBMU;

A BYTE is just a renaming of a char type. There was a typedef for this eariler in the code.
The member varable decleartion is unusal and I don't understand what it means. Does anyone know what this is doing?

yeah, i am surprised.

It's a bit field.

Sorry, bit feild? I don't think I have come across one before.

Material is 4 bits and the other is 6 bits.

Thanks. I think I understand it now