Definition,
An emulator is hardware or software that enables one computer system (know as the host) to behave like another computer system (know as the guest)
What is an Emulator in Android?
An Android emulator is an Android Virtual Device (AVD) that represents a specific Android device. You can use an Android emulator as a target platform to run and test your Android applications on your PC
It uses an open source processor emulator technology called QEMU.