What are LB, HB, UB, and MB in hex data?

I have a question in the code below.

I know as follows.

Hex 00FC = Decimal 252.  (Note:  High byte(HB) is 00.  Low byte(LB) is FC.)  
Hex 0565 = Decimal 1381.  (Note:  High byte(HB) is 05.  Low Byte(LB) is 65.)

I have confirmed that there are additional UB, MB.

{

    UINT32 dwData;

    ...
    ...     


    dwData.Val = 0x00000101;

    ...
    ...

    //Write Bytes
    WriteByte(dwData.byte.LB);
    WriteByte(dwData.byte.HB);
    WriteByte(dwData.byte.UB);
    WriteByte(dwData.byte.MB);

    ...
    ... 

}

What are LB, HB, UB, and MB?