A Light Dependent Resistor (LDR) is a type of variable resistor whose resistance decreases as light intensity increases. It is made of a semiconductor material that exhibits photoconductivity, meaning its electrical resistance changes based on the amount of light it receives. LDRs are commonly used in automatic lighting systems, light meters, and electronic circuits where light sensitivity is required. They are cost-effective, energy-efficient, and widely used in Arduino and IoT projects.