1. **State the problem:** Simplify or understand the expression $4\sqrt{x}$. 2. **Recall the definition:** The square root function $\sqrt{x}$ represents the principal (non-negative) square root of $x$. 3. **Expression explanation:** The expression $4\sqrt{x}$ means $4$ times the square root of $x$. 4. **No further simplification is possible** unless we know more about $x$. For example, if $x$ is a perfect square, we could simplify $\sqrt{x}$. 5. **Example:** If $x=9$, then $4\sqrt{9} = 4 \times 3 = 12$. **Final answer:** The expression $4\sqrt{x}$ is already simplified and represents four times the square root of $x$.