What is the meaning of Synthesizer?

An electronic musical instrument that creates its sounds with electronics and generally is played via a keyboard.

An electronic instrument consisting of a module, or a set of modules, that creates its sounds with electronics and does not have any keyboard.

An electronic circuit that generates an electronic signal oscillation with accurate timing from a reference oscillator.

An electronic device that generates electronic signal patterns to test an electronic circuit.

A software program that allows a computer to be used as a musical instrument – virtual instrument

a synthesizer

Source: wiktionary.org