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.