The term 'diamond units' refers to three different measurements used to measure the size and quality of diamonds. The first unit is 'OUTS, ' which is a four-letter measurement that is used to describe the shape of a diamond. The second unit is 'INNINGS, ' which is a seven-letter measurement that is used to describe the clarity of a diamond. The third unit is 'carats, ' which is a six-letter measurement that is used to describe the weight of a diamond. All three of these measurements are used to determine the value of a diamond.