Android Debug Bridge (ADB) is a versatile command-line tool that allows developers to communicate with an Android device. It enables users to execute various commands, install and uninstall applications, and access device logs, making it essential for debugging and testing apps. ADB operates in a client-server architecture, where the client runs on a computer, the server runs on the device, and they communicate over a USB or Wi-Fi connection. This tool is part of the Android SDK (Software Development Kit) and is widely used for app development and troubleshooting in the Android ecosystem.