An Optical Time Domain Reflectometer (OTDR) is a device used to analyze and troubleshoot optical fiber networks. It sends pulses of light into the fiber and measures the time it takes for the light to reflect back after encountering faults, connectors, or splices. This information helps technicians identify issues such as breaks or excessive loss in the fiber. OTDRs are essential tools in the telecommunications industry, as they ensure the integrity and performance of fiber optic cables. By providing a visual representation of the fiber's condition, they assist in maintaining high-quality data transmission and efficient network management.