An ADB is a command line tool which can be used to communicate with Emulator or Android Devices.
When your development machine needs to communicate with an Android Device it does so using ADB. It’s a process that is controlled by a command also known as adb.
The adb command works by talking to an adb server which runs in the background at port 5037. The server is also known as adb daemon or adbd.
Android Studio also talks to this server when it needs to run an app via an Android Device.
To work with ADB you need Android SDK.