Clipping was the shaving of a coin. This was done to get the precious metal the coin was made from and melt it down. Many coins from earlier times are in odd shapes, the result of years of cutting off slivers.
This was one of the ways the debasement of the currency took place.
It was one of the problems with specie. Since many coins were made from gold and silver, the metal itself as value. This gave the money intrinsic value but also presented temptation to cut pieces off.