In
physics, a
scalar is a one-dimensional
physical quantity, i.e. one that can be described by a single real number (sometimes signed, often with
units), in other words a scalar is a physical quantity that only has magnitude but no direction, unlike (or as a special case of)
vectors,
tensors, etc. which are described by several numbers which characterize magnitude and direction and a vector can be defined as a physical quantity that has magnitude and direction. Formally, a scalar is unchanged by
coordinate system rotations or reflections (in
Newtonian mechanics), or by
Lorentz transformations or space-time translations (in relativity). A related concept is a
pseudoscalar, which is invariant under
proper rotations but (like a
pseudovector) flips sign under
improper rotations. The concept of a scalar in physics is essentially the same
as in mathematics. A physical scalar field is one type of more general fields, like
vector fields,
spinor fields, and
tensor fields.