Lens blur refers to the effect created when a camera lens is unable to focus on all elements in a scene simultaneously. This results in certain areas appearing soft or out of focus, which can enhance the subject's prominence by isolating it from the background. This technique is often used in photography and cinematography to draw attention to the main subject while creating a pleasing aesthetic. Depth of field plays a crucial role in lens blur, as a shallow depth allows for more pronounced blurring of the background, contributing to a more artistic composition.