The coefficient of friction is a numerical value that represents the amount of frictional force between two surfaces in contact. It is calculated by dividing the force of friction by the normal force pressing the two surfaces together. This value helps to determine how easily one surface can slide over another, with higher values indicating more friction. There are two main types of coefficients: the static coefficient of friction, which applies when surfaces are not moving relative to each other, and the kinetic coefficient of friction, which applies when they are sliding. The coefficient varies depending on the materials involved, such as rubber on asphalt or ice on metal.