A speedlight is a portable flash unit used in photography to provide additional light when needed. It can be mounted on a camera or used off-camera to create various lighting effects. Speedlights are popular for their versatility, allowing photographers to adjust the intensity and direction of the light, which helps in achieving the desired exposure and mood in images. These devices often come with features like adjustable power settings, zoom capabilities, and wireless triggering options. Many speedlights are compatible with different camera brands, making them a valuable tool for both amateur and professional photographers looking to enhance their photography skills.