The term speed is commonly defined as follows:
Speed, being a scalar quantity, is the rate at which an object covers distance. The average speed is the distance (a scalar quantity) per time ratio. Speed is ignorant of direction. On the other hand, velocity is a vector quantity; it is direction-aware. Velocity is the rate at which the position changes.
Then see: http://www.statisticshowto.com/scalar-definition/ Can a Scalar be Negative?
A number like -10 can be a scalar or a vector depending on what situation you are using it in. In linear algebra, scalars can be negative. A negative scalar like -10 would result in a vector in the opposite direction. In physics, scalars and vectors are defined by what happens to them during rotations. Direction is sometimes denoted with a + or – to mean the positive or negative direction relative to a reference point. In this situation, -10 would not be a vector as -10 would mean 10 units in the negative direction from the reference point. To avoid confusion, the word “scalar” in physics is sometimes limited to complex numbers.
For an example of confusion see: https://www.wired.com/2014/06/whats-the-difference-between-speed-and-velocity/
Also 'speed' is also often defined as the magnitude of the velocity vector, and it seems like this can lead to confusion.
My question is: Is there an agreed upon physics definition of the term 'speed'? For example, can the speed variable be negative or does it have to be preceded by a negative sign?