The square root of 81 is 9. This means that when you multiply 9 by itself (9 × 9), the result is 81. The square root is a fundamental mathematical concept that finds the original number that was squared to obtain a certain value. In various applications, square roots are used in geometry, algebra, and even in real-world problems involving areas and dimensions. It is one of the important operations in arithmetic and helps in simplifying expressions, solving equations, and understanding properties of numbers effectively. Both perfect squares like 81 and non-perfect squares exist in the realm of square roots.