An OTDR, or Optical Time Domain Reflectometer, is a device used to test and analyze fiber optic cables. It sends pulses of light into the fiber and measures the light that is reflected back. This helps technicians identify faults, splices, and connectors along the cable, ensuring optimal performance. OTDRs are essential tools in the telecommunications industry, as they provide valuable information about the quality and integrity of fiber optic networks. By pinpointing issues, they help maintain efficient data transmission and reduce downtime, making them crucial for network maintenance and troubleshooting.