(arithmetic) The symbol + used to denote the operation of addition, to indicate that a number is positive, and so on.

plural of plus sign

(mathematics) the symbol ∓, meaning "minus or plus", used alongside the plus-minus sign to show that a negative value is to be taken where the positive value is indicated by the plus-minus sign, and vice versa (as in (x ± 1) / (x ∓ 2), which means (x + 1) / (x - 2) and (x - 1) / (x + 2)).

plural of minus-plus sign