Hard Light
Hard light creates shadows with a sharp edge. There is a negligible transition from light to dark. Hard light is created by strongly focussed light travelling from a small (or relatively small), single-point light source like the Sun, a focussed beam of light, or an undiffused light bulb).
Hard light is found where the lighting is direct, undiffused, and is not bouncing or scattered by local objects or conditions. The flash on your camera is a hard light source. When direct and undiffused by clouds the sun is also a hard light source. A hard light source is relatively small and/or large and distant.

Hard light creates sharp lines with little or no
graduation of the shadows from light to dark.

Hard light is generated from a small point-source of light that sharply focusses the beam. It creates sharp, harsh shadow lines in the subject.
Photokonnexion pages:
Light and Lighting – Resource pages on Photokonnexion
Softbox (photographic glossary)
Make soft light work for you…
Soft Light (Information and use)
Soft Light (Definition)
Hard Light (Information and use)
Hard Light (Definition)
See the quality of the light
On the web:
Virtual lighting studio by zvork (interactive)
The importance of eggs