Most prescriptions will only contain 3 of these elements, however in some prescriptions additional elements are required depending on the type of lenses.
SphereThis is the power that is required to correct long and short sighted prescriptions. This may be positive (+), negative (-) or perhaps zero (Plano).
Base CurveThis element represents the curvature of the lenses, which ultimately corresponds to the curvature of your eyes. This may be different for each eye, however this value must be listed on your prescription for it to be valid.
DiameterThe diameter represents to size of the lenses. This may be different for each eye, however this value must be listed on your prescription for it to be valid.
Other elements that may be present on your contact lens specification would include all of the above plus one or more of the following elements, depending on the type of lenses required.