The purpose of a self-driving car's LiDAR system is to provide accurate 3D mapping and obstacle detection. LiDAR (Light Detection and Ranging) uses laser pulses to measure distances between the vehicle and surrounding objects. By creating a detailed spatial representation of the environment, the LiDAR system helps autonomous vehicles navigate safely, identify obstacles, and make informed driving decisions. This technology complements other sensors like cameras and radar to achieve a comprehensive understanding of the vehicle's surroundings, critical for autonomous driving.