minus-plus sign

Wiktionary

1. n. 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)).