The expression "(x_2 - x_1)" represents the difference between two values, x_2 and x_1. In mathematics, this is often used to calculate the change or distance between two points on a number line or in a coordinate system. It helps in understanding how much one value differs from another. This concept is widely applicable in various fields, such as physics, where it can represent changes in position, or in economics, where it can indicate changes in price. By analyzing "(x_2 - x_1)", one can gain insights into trends and relationships between different variables.