Fill Light - Lighten shadows and control Contrast and Lighting Ratio.
Key light (main light) - The key light can determine the mood.
Hair light - An accent light presumably limit to the top of the head.
Background light - Separates subject from background.
Shadowless -power of shadows is to reveal and hide/conceal.
Hard Light - A small, direct, usually focusable source, with or without lens, that produces strong High-lights and dark shadows.
Soft light - Diffused bounced, indirect; opposite of hard light.
Grey card - A matte (18%') reflected card.
Reflection - Out of control reflections can hurt your image or controlled ones can enrich it.
Diffuser - Reduce contrast and increase beam angle.
Intensity - The strength of the incident light independent of subject reflectivity.
3:1 lighting ratio - occurs when the light lacks compatibility between two light sources is one and a half f-stops.