So close yet so far. If only you had read ONE more paragraph.
Every nonnegative real number x has a unique nonnegative square root, called the principal square root or simply the square root (with a definite article, see below), which is denoted by √x where the symbol “√” is called the radical sign or radix.
This sentence made no sense to me as it directly contradicted the previous one. But it’s just a confusion on my part between the function called square root, which confusingly outputs two different numbers called “square roots”, and “the” number called square root; I’ve edited my comment. Thanks for correcting me!