Surround-sound is a way of playing sound through four or more speakers placed around the room — in front of you, beside you, behind you — so that the sound seems to come from every direction, the way it does in real life. When a car drives past in the film, you hear it move from your left ear to your right. It is what makes a cinema feel like a cinema. You will see it written three ways — surround sound, surround-sound, and just "surround" in equipment descriptions — and the hyphen usually appears when the phrase sits in front of a noun: "a surround-sound system". You will also meet numbers: 5.1 means five speakers plus one bass box, 7.1 means seven plus one. Nowadays good headphones and phones can fake it with software, and people still call that surround sound even though there are only two real speakers. It is an everyday word, not a technical one — you can say it in a shop without sounding like an engineer.