Final answer:
Sfumato is the process of blurring outlines in painting by subtle tonal variations to create a smoky effect. It is used to blend objects in the foreground into the background and give the illusion of depth.
Step-by-step explanation:
The process of blurring outlines in painting by subtle tonal variations so that objects in the foreground blend into the background is called sfumato. Sfumato is the application of translucent layers of paint to create a smoky and seamless effect. This technique, used by artists like Leonardo da Vinci, gives the illusion of three-dimensionality and depth in a painting.