Noun

1. the symbol ±, meaning "plus or minus", used to indicate the precision of an approximation (as in "The result is 10 ± 0.3", meaning the result is somewhere between 10 - 0.3, that is, 9.7, and 10 + 0.3, that is, 10.3), or as a convenient shorthand for a quantity with two possible values of opposing sign and identical magnitude (as in "The roots of the equation x² - 4 = 0 are ±2").