The stereo reproduction technique allows us to produce stereophonic sound. This is achieved by playing two independent sound sources simultaneously through the 2-channel speakers or stereo headphones. In this way, the listeners can perceive a multidirectional sound.
Clement Ader demonstrated the first ever 2-channel sound system back in Paris in late 19th century. This is one of the early origins of stereophonic technology. In 1930s, a British engineer Alan Blumlein invented an audio recording technique which is by placing two dipole microphones at 90º angles from each other so that the microphones can record from the front and the rear of the sound source and when they are placed correctly, in the final recording, the listeners can perceive the different directions of the sound.
References:
Alan Dower Blumlein, the Forgotten Engineer With 128 Patents