Negative magnification refers to the situation in optics where the image produced by a lens or a mirror is inverted relative to the object. When the magnification is negative, it indicates not only that the image is flipped but that it may also be of a different size than the object. This typically occurs in concave mirrors or when viewing an object through certain types of lenses under specific configurations.
On the other hand, magnification that is less than 1 in magnitude means that the image being produced is smaller than the actual object. A magnification of, say, 0.5 means that the image is half the size of the object. This often happens in cases where lenses or mirrors are set to focus on distant objects, rendering them smaller in the viewfinder or projection.