A square root of a number is a value that, when multiplied by itself, gives the original number. For example, the square root of 9 is 3 because 3 × 3 = 9. Square roots can be positive or negative, but the principal square root is the non-negative one. Square roots are often represented using the radical symbol (√). For instance, √16 equals 4. Square roots are useful in various fields, including mathematics, engineering, and science, as they help solve equations and understand geometric concepts like the length of a side in a square.