A bulb is a device that produces light when electricity passes through it. The most common type is the incandescent bulb, which uses a thin wire called a filament that glows when heated. Other types include LED (Light Emitting Diode) bulbs, which are energy-efficient and have a longer lifespan, and CFL (Compact Fluorescent Lamp) bulbs, which use gas to produce light. Bulbs come in various shapes and sizes, designed for different purposes, such as household lighting, automotive use, or decorative displays. They are typically fitted into fixtures that hold them in place and connect them to a power source, allowing for easy installation and replacement.