a (mathematics|of an expression, equation(,) or function) Containing only numbers, letters(,) and arithmetic operators.
a (mathematics|number theory) (context|said of a number) Which is a root of some polynomial whose coefficients are rational.
a (chess|of notation) Describing squares by file (referred to in intrinsic order rather than by the piece starting on that file) and rank, both with reference to a fixed point rather than a player-dependent perspective.