A correct exposure has detail in the highlights and shadows. Correct exposure means an image with maximum detail, that gives us the most options in editing.
In this image the highlight or lightest areas (the clouds) have lots of detail with no ‘blown out’ areas.
Too much light leads to overexposure:
images that are too bright and have no detail in the light or highlight areas.
Too little lights leads to underexposure:
images that are too dark and have no detail in the dark or shadow areas.