The expression "x_2 - x_1" represents the difference between two values, often used in mathematics and statistics. Here, x_2 is the final value, while x_1 is the initial value. This calculation helps determine how much one value has changed compared to another. In various applications, such as physics or economics, "x_2 - x_1" can indicate changes in position, temperature, or financial metrics. Understanding this difference is crucial for analyzing trends, making predictions, and assessing performance over time.