In phyics a scalar quantity is a quantity that is described solely, from a mathematical point of view, by a “scalar,” that is, by a real number associated with a unit of measurement (examples are the following: mass, energy, temperature, etc.).
The definition of “scalar” derives from the possibility of reading the value on a graduated scale of a measuring instrument, as it does not need other elements to be identified.
The concept of a scalar in physics is essentially the same as in mathematics. In mathematics a scalar is an element of a field which is used to define a vector space. A quantity described by multiple scalars, such as having both direction and magnitude, is called a vector.