Firebase is a backend-as-a-service platform developed by Google that facilitates custom mobile application development, offering various features like real-time databases, authentication, cloud functions, and storage. Its ease of setup, security, and integration capabilities have made it a preferred choice among mobile app developers, with notable users including The New York Times and Duolingo. Firebase supports features for growth and user engagement while ensuring seamless data synchronization and management without the need for server-side infrastructure.