The equal sign (=) is a mathematical symbol used to indicate that two expressions have the same value. It is commonly found in equations, where it separates the left side from the right side, showing that both sides are equivalent. For example, in the equation 2 + 2 = 4, the equal sign tells us that the sum of 2 and 2 is the same as 4. The equal sign was first introduced in 1557 by the Welsh mathematician Robert Recorde. He chose the symbol because he believed that no two things could be more equal than parallel lines. Today, the equal sign is a fundamental part of mathematics, used in various fields such as algebra, calculus, and computer programming.