A progress bar is a visual indicator that shows the completion status of a task or process. It typically appears as a horizontal or vertical bar that fills up as the task progresses, providing users with a clear understanding of how much work has been done and how much is left. Progress bars are commonly used in software applications, file downloads, and installations. These bars can vary in design, with some displaying percentage values or estimated time remaining. They help improve user experience by managing expectations and reducing uncertainty during tasks, such as when using computer programs or downloading files from the internet.