For the uninitiated, leading is the vertical distance between the baselines of each line of type. That is where a letter sits, which requires a deeper explanation I will put into an article soon. Either way, the closest correlation between this value is the CSS attribute of line-height.
Here is how we convert leading into line-height:
line-height = 100 * ( leading / font-size)
0.2 = 100 * ( 72 / 26 )
The Photoshop Leading Style toggle is where you go to map to line-height.