Portrait Lighting Definitions

Three-point Lighting- Consists using three separate lighting sources such is a key light, usually the strongest light on set. A fill light, which fills the shadows being casted by the key light, and the backlight, which creates a contour.

http://www.ourpicz.com/three-point-lighting-for-portrait-photography/

http://www.animationtutorial.in/2013/03/20/introduction-3-point-lighting-maya/

Butterfly- When a single light source is placed directly in front of the subject, above the subject and camera, creating a downward shadow on the subject giving him/her a shadow beneath the nose and cheeckbones. Often used in fashion and glamorous portrait shots.

http://zealfaith.wordpress.com/2011/08/23/tc-butterfly-lighting/

http://photo.stackexchange.com/questions/6772/what-is-butterfly-lighting-and-when-do-i-use-it

Loop Light- Created by placing a light above the subject slightly to the right or left, casting a rounded shadow beneath the subjects nose on their cheek.

http://blog.lindsayadlerphotography.com/intro-to-studio-lighting-diagrams

Silhouette- This use of light consists of the background of the subject being much brighter, making the subject darker and creates a form.

http://www.flickr.com/photos/zxdphotography/1805260019/

http://facweb.cs.depaul.edu/sgrais/lighting_styles.htm