A brolly is a lighting modifier for professional flash systems. It’s designed to provide a much larger, softer light source than a naked flash head, and it’s one of the most popular lighting accessories.
It’s just like a regular umbrella, but the inner surface is highly reflective. The flash is positioned to point directly into the inside of the brolly and this surface reflects the light back to the object or scene you’re photographing.
The inner surface may be white or silvered, and the brolly has a metal shaft which slides into a clamp on the flash head.