What is meant by a "scalar quantity"?

A scalar quantity is defined as one that possesses magnitude but lacks direction. This means it is described solely by its size or numerical value. For instance, temperature and mass are scalar quantities; you can specify that an object has a mass of 5 kilograms or that the temperature is 20 degrees Celsius without needing to indicate a direction.

In contrast, vector quantities, which involve direction, would include values like velocity and acceleration, where both magnitude and direction need to be specified. Therefore, the correct characterization of a scalar quantity is that it is one that includes size only, distinguishing it from vector quantities which are dependent on both magnitude and direction.