Shutter speed is the time that your camera shutter is open, its basically how long your camera spends taking a photo.It is measured in seconds such as 30,15,1,1/10,1/30,1/250 a high shutter speed such as 30 will allow you to show lots of movement such as water flowing whereas a low shutter speed will allow you to quickly capture the scene as if it were frozen this would be best if you need to quickly capture somthing an example of this is in sport as you do not want ghosting and random thing noving around in your picture.