- (mathematics) The number which, when squared, yields another number.
- The square roots of 4 are 2 and −2, the square root of 0 is 0, and the square roots of −4 are 2i and −2i.
- (mathematics) The positive number which, when squared, yields another number; the principal square root.
- The square root of 4 is 2. No negative real square roots exist. Negative numbers have no real square roots.
Even in mathematical contexts, square root generally means positive square root. If there is a chance of ambiguity, prefer constructions like a square root or a complex square root to indicate the first definition, or the positive square root or similar to indicate the second sense.