The above-mentioned error is caused when the Command prompt or PowerShell is not able to identify the ADB command. We will have a look at the various steps to fix this “adb not recognized” error. Among them, the most common is “adb” is not recognized as an internal or external command, operable program or batch file. But more often than not, some of the other errors do creep in. These include unlocking the bootloader, installing a custom recovery, booting your device to recovery or fastboot mode, installing APKs, etc. Some of the most important Android customizations are possible thanks to these ADB commands.
It basically creates a bridge that allows for successful communication between your Android device and PC.
ADB or Android Debug Bridge is a command-line tool, part of the Android SDK and Platform Tools.