Can anybody to me what exactly does the bwarea() function do in matlab.

The help manual says the following:

• Patterns with zero on pixels (area = 0)
• Patterns with one on pixel (area = 1/4)
• Patterns with two adjacent on pixels (area= 1/2)
• Patterns with two diagonal on pixels (area= 3/4)
• Patterns with three on pixels (area = 7/8)
• Patterns with all four on pixels (area= 1)

I don't quite get this. what does it mean "patterns" ????