Blur caused by the camera moving during the exposure. It is most common when you hold the camera in your hands and use a slow shutter speed, a long lens or low light. The whole image looks soft, not just a moving subject.
To avoid it, use a shutter speed that is fast enough. A common rule of thumb is at least 1 divided by the focal length, for example 1/200 second with a 200mm lens. Image stabilization, a tripod, or a self-timer or remote release also help.
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