The square root of 9 is 3. This means that when 3 is multiplied by itself, the product obtained is 9. It is important to note that there are two possible solutions for the square root of any positive number, one positive and one negative. However, conventionally, when we write the square root of a number, we usually refer to only the positive solution. In the case of the square root of 9, the negative solution would be -3, because -3 multiplied by itself also equals 9.