OD - OD stands for oculus dexter, the Latin phrase for "right eye".
OS - OS stands for oculus sinister, the Latin phrase for "left eye".
Base Curve (BC) - The base curve determines what type of fit is required for the lens to meet the curve of your eye. This is usually written in millimeters or sometimes with the words: flat, median or steep.
Diameter (DIA) - The diameter of a lens determines what length of width best fits your eye. It measures the width of a lens in millimeters, from end to end.