1. **State the problem:** Simplify or understand the expression $\sqrt{x}$. 2. **Formula and rules:** The square root function $\sqrt{x}$ gives the number which, when multiplied by itself, equals $x$. It is defined for $x \geq 0$ in the real numbers. 3. **Intermediate work:** If $x$ is a perfect square, say $x = a^2$, then $\sqrt{x} = \sqrt{a^2} = a$. For example, if $x=9$, then $\sqrt{9} = 3$. 4. **Explanation:** The square root symbol $\sqrt{\cdot}$ means "what number times itself equals the inside value?" For any non-negative $x$, $\sqrt{x}$ is the principal (non-negative) root. 5. **Final answer:** The expression $\sqrt{x}$ represents the principal square root of $x$, which is the non-negative number whose square is $x$.