A short, everyday word for a synthesizer — the electronic keyboard-type instrument that makes sounds electronically instead of from strings or air. Nobody in the music world says the long word much; 'synth' is what musicians, producers and fans actually say. It is a countable noun ('he bought an old synth', 'three synths on stage'), and it is casual but not slang — you would see it in a music magazine or a shop listing without any trouble. It also gets used before another noun to describe a sound rather than an object: 'synth sound', 'synth line', 'synth bass'. And it lives inside the name of a whole style of music, synth-pop — the bright electronic pop of the 1980s that Taiwanese listeners will know from a-ha, Depeche Mode, and more recently from anything that deliberately sounds retro. One more thing worth knowing: because a synth can imitate other instruments, people sometimes use 'synth' with a slight sneer, meaning 'not the real instrument' — 'those aren't real strings, that's just a synth'. Whether that is an insult depends entirely on who is talking.