MAC BOOK PRO

[VaShaun Jones]

IF THERE IS ANYONE OUT THERE THAT HAS A MAC BOOK PRO AND CAN TELL ME  
WHAT THIS SMALL RECTANGULAR HOLE IS ON THE RIGHT SIDE OF MY COMPUTER I  
WOULD APPRECIATE IT. IF YOU ARE FACING THE NOTEBOOK WITH IT OPENED AND  
START YOUR FINGERS DOWN THE RIGHT SIDE OF THE BOTTOM HALF OF THE  
COMPUTER UNTIL YOU GET TO A OPENING, RIGHT BEFORE THE FIRST USB PORT.  
DOES ANYONE KNOW WHAT THIS IS USED FOR?