Big endian refers to a storage of values beyond one byte. It's also known as MSB (most significant byte). It's a contrast to little endian which stores in the opposite fasion. In big endian, the order of the bytes which are stored are not changed.
The 16-bit value $4782 would be stored as $47 $82, and the 24-bit value $426955 would be stored as $42 $69 $55. Notice how the byte order does not change. This is how big endian works.