A pinguecula is a yellowish patch or bump on the conjunctiva, most often on the side closest to the nose. It is a change in the normal tissue that results in a deposit of protein, fat and/or calcium. It is similar to a callus on the skin.
A pterygium is a growth of fleshy tissue, often arising from a pinguecula, on the conjunctiva that extends over the cornea. This growth may remain small or grow large enough to interfere with vision.