A synthesizer is an electronic musical instrument that creates sounds by generating and combining electrical signals. Unlike traditional instruments that make sound through vibrating strings, air columns, or drumheads, a synthesizer produces sound electronically and can imitate almost any instrument or create entirely new sounds that never existed before.

When someone plays a synthesizer keyboard, they might make it sound like a piano, a trumpet, or a choir of voices. But they can also create sounds no acoustic instrument could ever make: whooshing space sounds, rumbling bass notes that seem to shake the floor, or shimmering tones that sound like crystals singing. Many popular music producers and composers use synthesizers to create the background music, sound effects, and beats you hear in songs, movies, and video games.

Early synthesizers were huge machines that filled entire rooms and required patch cables to connect different sound-generating modules. Today's synthesizers can be small keyboards or even software programs on computers, but they all work by synthesizing sound from basic electronic signals.

Some famous synthesizer sounds include the electronic melodies in 1980s pop music and the deep bass “drops” in modern electronic dance music. Synthesizers opened up new possibilities for musicians, letting them become sound designers who could imagine any sound and then create it.