Action sequence photography is taking a bunch of photos from the same place of the motion of a subject and combinding all of the images together in photoshop. Here is a tutorial on how to do it:
Basically, you put each picture as a different layer, make them mask layers and color black on the mask of the higher layers in order to reveal the pictures in the previous layers.
This technique is used mostly in extreme sports with still backgrounds such as skateboarding, motorcross, BMX, snowboarding, and parkour.
It can also be used in other sports to show the path of a ball/puck.
here are some examples: