The document discusses square roots and how to estimate them. It defines a square root as a number that, when multiplied by itself, gives the original number. It also defines perfect squares as numbers with whole number square roots and rational numbers as integers, fractions, and perfect squares, while irrational numbers are square roots of non-perfect squares. The document recommends estimating square roots by finding the perfect squares above and below the given number and taking the square roots of those numbers.