Latency is delay.
The time between when you push your foot on the brake pedal of your car and the actual brake pads press into the wheel discs is known as your vehicle braking system latency . Latency is just as much an issue in audio hardware and software. When you press play on your CD player, there is always a delay before the music starts. This may not matter for someone at home, but a DJ must be able to precisely control when they start a song. It's not just playing and stopping a song that matters either.