The speaker discusses a classic mathematical problem of finding the area under a curve between two boundaries on the x-axis. They explain the process of approximating this area by dividing it into smaller sections using delta x. Each section is represented by a rectangle with a width of delta x and a height determined by the function value at a specific boundary. By summing up the areas of these rectangles, an approximation for the total area can be obtained. The speaker emphasizes that this approximation can be improved by making delta x smaller and increasing the number of rectangles. They hint at the concept of taking the limit as delta x approaches zero and the number of rectangles approaches infinity for a more accurate result.