Definition
1. the act of igniting or illuminating.
2. the arrangement of lights to achieve particular effects.
3. an effect achieved by the arrangement of lights.
4. the way light falls upon a face, object, etc., esp. in a picture.
( link: http://www.thefreedictionary.com
/lighting)
Comments
This picture is a brilliant example of side lighting. it is used a lot in portraits to highlight distinctive features on the face e.g. wrinkles, creases, bone structure and to give the face more character and interest and can be achieved by lighting from the side of the face or placing your subject by a window. as well as side lighting, there are many other methods to use (see slideshare below), for example, back lighting, natural lighting and broad lighting.
3 Point Lighting for Photography from 614209
This slideshare is very useful for referencing as it goes into detail about how to achieve the techniques of lighting and when would be appropriate to use them.