The Rule of Thirds is a fundamental principle in photography composition where the frame is divided into thirds both horizontally and vertically, creating nine equal parts. The main idea is to position the key elements of the image along these lines or at their intersections to create a harmonious and balanced composition. By placing the subject or focal point off-center, the Rule of Thirds helps to draw the viewer's eye into the scene and create a more interesting and dynamic image. This technique is widely used in photography to create visually appealing and well-balanced shots.