An Objective Function is a mathematical expression used in optimization problems to define the goal of the problem. It quantifies what needs to be maximized or minimized, such as profit, cost, or distance. The objective function takes variables as inputs and produces a single value that reflects the performance of a given solution. In the context of operations research or machine learning, the objective function guides the search for the best solution among many possibilities. Techniques like linear programming or gradient descent are often employed to find the optimal values of the variables that yield the best outcome according to the objective function.