X—indicates the maximum scalability of the processor.
1000 Series = 1-way servers and workstations
2000 Series = Up to 2-way servers and workstations
8000 Series = Up to 8-way servers and workstations

Y—indicates socket generation. This digit is always ‘2’ for AMD Opteron processors for Socket F (1207) and Socket AM2.
1000 Series in Socket AM2 = Models 12XX
2000 Series in Socket F (1207) = Model 22XX
8000 Series in Socket F (1207) = Model 82XX

ZZ—indicates relative performance within the series.
An AMD Opteron Processor Model 2218 is higher performing than an AMD Opteron™ Processor Model 2216, etc.

HE—indicates a 68W low-power AMD Opteron™ processor.
Performance of a low-power AMD Opteron processor HE model number, XYZZ, is equal to the performance of the same model number standard-power version. For example, an AMD Opteron processor Model 2216 HE offers the same performance as a standard wattage AMD Opteron processor Model 2216.

SE—indicates a higher power, frequency-optimized AMD Opteron™ processor.
Performance of an AMD Opteron™ processor SE model number, XYZZ, is equal to the performance of the same model number standard-power version. For example, an AMD Opteron processor Model 2220 SE offers the same performance as a standard wattage AMD Opteron™ processor Model 2220 -- however Model 2220 SE will be available at an earlier date than the standard power model.

The chart below further explains the differences between AMD Opteron™ processor Series and Model Numbers.