A scalar quantity is a physical measurement that is described by a single numerical value, which represents its magnitude. Scalars do not have a direction associated with them, making them simpler to understand and work with. Common examples of scalar quantities include temperature, mass, and time. In contrast to scalar quantities, vector quantities have both magnitude and direction. For instance, while speed is a scalar that tells you how fast something is moving, velocity is a vector that indicates both the speed and the direction of that movement. Understanding the difference between scalars and vectors is essential in fields like physics and engineering.