The Rectangular Marquee Tool is a selection tool found in graphic design software like Adobe Photoshop. It allows users to create rectangular or square selections within an image. By clicking and dragging the cursor, users can define the area they want to work on, making it easier to edit or manipulate specific parts of an image. This tool is particularly useful for tasks such as cropping, copying, or applying effects to a selected area. Users can adjust the selection by holding down the Shift key for a perfect square or the Alt key to draw from the center.