WOF - Width of Fabric.  This is generally a strip of fabric that is cut from selvage edge to selvage edge of the fabric.  The width of most quilting fabric is between 40" and 44".

 Fat Quarter - This is a piece of fabric that is generally 18" X 22" in size.  A quarter yard of fabric is 9" by WOF (see above).  A Fat Quarter will allow you to cut bigger pieces from the same amount of yardage.