Aperture size refers to the opening in a camera lens that allows light to enter. It is measured in f-stops, with a lower f-stop number indicating a larger opening. A larger aperture lets in more light, which is useful in low-light conditions and can create a shallow depth of field, blurring the background while keeping the subject in focus. In contrast, a smaller aperture allows less light to enter, resulting in a greater depth of field. This means more of the scene will be in focus, which is often desired in landscape photography. Understanding aperture size is essential for controlling exposure and achieving desired artistic effects in photography.