Scalar usually refers more simply to a variable that can be represented on a graduated scale.
However, it may be good for biologists to begin to get familiar with this other meaning of scalar:
(See standard descriptions of quaternion math in e.g. wikipedia.)
Quaternions are at an intermediate level of complexity in the mathematics of the complex algegras -- NOT a subject typically taken up in biology.
Of possible great relevance to the future of biology, however, is the fact that Maxwell's original equations describing light were in quaternion notation and that the "scalar" elements are left out in the now standard subsequent descriptions given in vector notation. It has been presumed that these scalar elements are only relevant in regions of significant space-time curvature (e.g. early in the Big Bang, near black holes, etc...). However, different rules may turn out to apply (perhaps only under certain circumstances) in biological systems.