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The term frame dragging refers to certain general-relativity (GR) effects on inertial reference frames near rotating massive objects. The effects have been described as the adjacent space rotating as well, the highest rotation frequency being nearest the object, as if space is being stretched to rotate. The effect is extremely slight other than around rotating compact objects, in particular, around rotating black holes. The term ergosphere refers to the volume surrounding a rotating black hole where the dragged space is moving the speed of light or faster in relation to distant space, e.g., to us. Gravitoelectromagnetism is a model that captures these effects; the term uses the word "magnetism" because some of the GR effects are analogous to magnetism's relation to electricity.