In photography shutter speed is one of the most basic important controls on a digital cameras. It controls the amount of time that your photo  is exposed to light. Shutter speed, is measured in seconds, but often marked in reciprocal seconds.

photo by werkunz1

Adjustment to the aperture controls the depth of field, the distance range over which objects are acceptably sharp; such adjustments generally need to be compensated by changes in the shutter speed.

By using shutter speed you can freeze action or show the passage of time in your photos.

If you want to show fast motion in your photos you have to use a fast shutter speed

If you want to show slow motion in your photos you have to use a slower shutter speed.

So you can ask what are the speed we can use in digital camres.. Here is an example of shutter speed numbers, from fast to slow:  

Piazza Ferrucci at the speed of light

1/2000 second,
1/2000 sec,
1/500 sec,
1/250 sec,
1/125 sec,
1/60 sec,
1/30 sec,
1/15 sec,
1/8 sec,
1/4 sec,
1/2 sec,
1 second.

On some digital cameras you can manually set shutter speed a lot slower than a second for very long exposures.