A variable is a characteristic or factor that can change or vary in different situations. For example, in a scientific experiment, the temperature, time, or amount of a substance can be considered variables. These changes can affect the outcome of the experiment, making it important to identify and control them. In mathematics, a variable often represents an unknown value, typically denoted by letters like x or y. By using variables, mathematicians can create equations and formulas that describe relationships between different quantities, allowing for problem-solving and analysis in various fields, including science, economics, and engineering.