Butterfly lighting, also known as paramount or glamour lighting, is a common type of lighting used in a studio for portraits. It is called butterfly lighting because of the shadow that forms on the nose looks like a butterflies wings. The lighting comes from above the camera.
Butterfly lighting is was to photograph classic Hollywood stars. It highlights cheekbones and neck and creates shadows below them which makes the model look thinner.
You can use flash light connected to the camera or you can use a continuous light. It can be natural or artificial, soft or hard it depends on the result you would like.
You can also use reflectors to bounce the light back up and soften the shadows.