Simple and pure shear are two important varieties of strain. Simple shear is a three-dimensional constant-volume strain (Twiss and Moores, 1992; Ferguson, 1994; Davis and Reynolds, 1996). It is analogous to the process that occurs when you place a deck of cards on a table and then gently pressing down on the top of the the deck move your hands to the right or left. As you move your hand the top of the deck slides over the lower part, with each successively intervening card sliding over its lower neighbor.
In contrast to simple shear, pure shear is a three-dimensional constant-volume "homogeneous flattening" (Twiss and Moores, 1992). During homogeneous flattening a sphere is transformed into a pancake-like shape and a box is changed into a tablet or book-like form.
After viewing the animations for constant volume simple and pure shear I hope that you observed that the dimension of the distorting body that was parallel to the y-axis never changed. Such results are characteristic of plane strain. Visual 2D Strain, the program that accompanies this tutorial was developed primarily for the study of plane simple and pure shear.