This is one of the three parameters that controls exposure. It controls the amount of time during which your shutter is open and your sensor is exposed to a light that goes through the lens. This property is expressed in fractions of a second.
When controlling shutter speed, you have to always remember about your Crop factor and focal length of your lens, because these affect the sharpness of your photographs. Because of that you need to know your shutter speed limit for handheld photographs. However, if you want to make sure that the subject that you photograph is frozen in time and there’s no blur motion, you have to increase the shutter speed 2 or 3 times above your handheld limit, or whatever is required to freeze the subject.