Some element of the picture is moving, it may be the camera, the subject or the light, or all three.
 
I like to experiment with the camera to see what it can capture, there are a lot of misses but sometimes it works out and you get an interesting result. Digital cameras are good for that although three of the images on this page were taken on film, experimenting on film can get a little expensive. The only filter is a Neutral Density, allowing me to get longer shutter speeds on bright days.