A fast shutter speed is typically whatever it takes to freeze action. If you are photographing birds, that may be 1/1000th second or faster. However, for general photography of slower-moving subjects, you might be able to take pictures at 1/200th second, 1/100th second, or even longer without introducing motion blur.
Here are examples of the internet.
The photo is taken with the focus on the car. The blurriness shows how fast the object is.
What is the best shutter speed?
The average camera speed is usually 1/60. Speeds slower than this are hard to manage as they almost always lead to blurry photographs. The most common shutter speed settings available on cameras are usually 1/500, 1/250, 1/125, 1/60, 1/30, 1/15.
Very long shutter speeds are used to intentionally blur a moving subject for effect. Short exposure times are called "fast", and long exposure times are called "slow". Adjustments to the aperture need to be compensated by changes of the shutter speed to keep the same exposure.