This is primarily applicable to drone imaging, because the drone is moving while taking photos. To avoid motion blur the camera must be stationary and stable or the images must be taken at a sufficient shutter speed. Shutter speed is a unit that defines how long is the cameras sensor exposed to light (hence another common synonymous term exposure time).
For example, if the image is exposed for one tenth of a second (expressed as 1/10 in all camera systems) this is considered a slow shutter speed. In this case any camera movement while taking an image at 1/10 speed will be blurred to a degree.
One should always try to maximize the shutter speed to make images free of motion blur. Distance to the terrain or object and speed of the drone are contributing factors, but as a rule of thumb do not go any slower than 1/250 shutter speed at any times when the aircraft is moving.