The shutter speed is the amount of time that the aperture will allow light to pass through the camera and burn the image. This value is represented in relation to one second and can range from values of 1/4000 of a second (or faster) to 30 seconds (or slower).
When a very fast shutter speed is used, lets say 1/2000 of a second, an image of a flying insect may appear to be completely motionless in the sky. When a very slow shutter speed is used, lets say 5 seconds, an image of a bike rider may appear to be smeared across your photograph also appearing somewhat transparent.
Below is an example of a very slow shutter speed – in this case around 10 second long. The result is a streak of light from the cars as they pass by.
Camera shake can be a very destructive and unwanted influence on your digital image. This is when an image appears blurry or not as crisp as desired because the photographer moved ever so slightly while the shot was being taken. This could be very unintentional and even caused by influences such as wind or an unsteady footing.
Generally a shutter speed slower than 1/60 of a second will require some additional stability to prevent noticeable camera shake. When a zoom lens is used the threshold increases because smaller amounts of camera shake is magnified in a zoomed image. When using telephoto lenses over 200mm or shooting at slower shutter speeds a tripod or monopod is recommended. If you are traveling you might even consider buying a bag of rice at your destination and using it as a stabilizer.