Auto-scaling is a cloud computing feature that automatically adjusts the number of active servers based on current demand. When user traffic increases, more servers are added to handle the load, ensuring that performance remains stable. Conversely, when demand decreases, unnecessary servers are removed to save costs. This process helps businesses maintain efficiency and reliability without manual intervention. Auto-scaling is commonly used in platforms like Amazon Web Services and Microsoft Azure, allowing organizations to respond quickly to changing workloads while optimizing resource usage and expenses.