The term 'PREFIX FOR METRIC' refers to two three-letter prefixes used in the metric system. The first prefix is 'GEO', which stands for 'geometric'. This prefix is used to denote a unit of measurement that is based on the geometry of a particular shape, such as a circle or a square. The second prefix is 'ISO', which stands for 'International System of Units'. This prefix is used to denote a unit of measurement that is based on the International System of Units, which is the most widely used system of measurement in the world.