Goal Seek, a feature in Microsoft Excel, is used to find the necessary input needed to achieve a specific result in a formula. For example, if you're working with a sales forecast that calculates total revenue based on units sold and you'd like to find out how many units need to be sold to meet a revenue target, Goal Seek can determine this for you. It is part of the What-If analysis tools in Excel and allows for solving unknowns without manually testing different inputs.

Using Goal Seek is straightforward. Users specify a cell containing a formula, the desired result for that formula, and the input cell that Excel should vary to reach the goal. Excel then iterates to find the input value that causes the formula to achieve the specified result. For instance, "If the formula =A1*B1 results in total revenue, and we desire the output to be $500, then Goal Seek can alter A1 to achieve this output." This feature saves significant time in scenarios involving trial and error calculations, providing immediate answers to such "what-if" analyses.

Goal Seek is often utilized in financial modeling, budgeting, and reconciliations, especially in month-end processes where precise estimations and adjustments are critical.