The perimeter of a square is given by the formula:
\[ P = 4s \]
where \( P \) is the perimeter and \( s \) is the length of one side of the square. If the perimeter is represented by \( x \), we can set up the equation:
\[ x = 4s \]
To find the length of one side \( s \), we can solve for \( s \) by dividing both sides by 4:
\[ s = \frac{x}{4} \]
Thus, the expression that represents the length of one side of the square is:
\[ \frac{x}{4} \]