Motion blur is capturing the rapid movement of a subject with a camera with a specific shutter speed that allows you to capture the object with some visual streaking that gives a clue towards the movement.
I picked this photo as my personal best because I found a bit of humor in the position we stood in and the emphasis on Calvin holding the bottle and the space in the hallway that framed the picture. I also felt that lighting was super nice in this picture as well so you can clearly see everyone in the picture. The shutter speed we used to take this picture was 0.5″