There are three things to consider when talking about light:
Quality of light
direction of light
Amount
Quality of Light
Light can be either hard, soft, but there are varying degrees of hard and soft light.
Characteristics of a hard light source:
Hard light will have heavy shadows: more accurately, hard light sources create very crisp lines of shadow with very little gradation. Because of this, images shot with a hard light source gives the subject the appearance of having more detail or texture.
Synonyms and / or descriptors used when talking about hard light:
Harsh light - because of the extra detail it creates
Direct light - because hard light comes from a direct single spot opposed to soft light which is indirect
Examples sources of hard light:
The sun
Flash
Unshaded light bulbs
Characteristics of soft light
A soft light source is best thought of as indirect or spread out light. Think of how light enters inside of your home through the window. That light is bouncing around and spreading out before it ever reaches the glass. Soft light can be identified by elongated shadows (more gradation).
Synonyms and/or descriptors used when talking about soft light:
Indirect
Diffused
Examples of soft light
Window light
Shade
Light bouncing off of a white or lightly colored wall
Cloudy or overcast days
Direction of light
The direction of light plays a huge role in the look of your photograph.
As an experiment photograph the same person or object from the front of, the side of, and behind your light source to see what happens. You will end up with three very different looking images. Notice where the light begins to fall off. Which image looks like it has the most depth? Which looks flattest?
Amount
The amount of light is self explanatory but should not be confused with the quality of the light. You can have both an abundance of soft light as well as hard light.
Picture a scene in heaven in a tv show or movie. It is always depicted with lots of bright light, but that light is soft!
Amount
Amount is simple. It's how intense your light source is. Thats it. Both hard and soft light sources can be very bright or very dim.