sse450

at the bottom of the chart you can read: 
 
 
Working Distance: Distance from the top of the lens barrel to the subject
 
Shortest shooting distance: Distance from the image sensor to the subject 
 
So the working distance is the distance between front lens and subject and the shortest shooting distance is the distance between focal plane (where the sensor is) and the subject.
 
Here is the chart with all distances for each lens.
 
http://www.fujifilm.com/products/digital_cameras/accessories/pdf/mcex_01.pdf