Why do some Audi models have an 'S' before the number?

I've noticed that some Audi models have an 'S' before the model number, such as the S4 or S5. What does this 'S' signify and what kind of performance upgrades can be expected from these models?

The 'S' in Audi models stands for 'Sport', indicating a higher performance and sportier version of the base model. These models typically have upgraded engines, suspension, and other performance enhancements.

The 'S' models are Audi's answer to the BMW M series and Mercedes-AMG models. They offer increased performance and handling capabilities for those seeking a more dynamic driving experience.

The 'S' models are also equipped with Audi's iconic Quattro all-wheel drive system, providing better traction and handling in various road conditions.