Which friction force opposes the motion of an object as it slides over a surface?

The friction force that specifically opposes the motion of an object as it slides over a surface is known as sliding friction. This type of friction comes into play when two solid surfaces are in motion relative to each other, and it acts to resist that motion. It is generally lower than static friction, which is the force that must be overcome to initiate motion between two surfaces at rest relative to each other.

While rolling friction involves rolling objects and is often much less than sliding friction, and fluid friction pertains to objects moving through a fluid, they do not directly describe the resistance encountered when one object slides over another solid surface. Sliding friction, therefore, is the most accurate term to describe the force resisting motion in this particular context.