A beauty dish is a light modifier that looks like a huge dish with a reflector in front of the flash tube / light bulb. This smaller reflector will bounce the light back into the dish itself and here it will be spread out and then be send in the direction of the subject.
Some people like the effect of the light seen in the eyes of their models.
Also, you can have a honeycomb grid attached to the front of the dish. a They also sometimes come with a white cover made of a kind of fabric with an elastic, so it can be mounted to the front of the dish, softening the light even more. These dishes are popular in the world of portrait photography.