The capacity section shows you the numbers behind the top percentage on the Battery Information screen. The “Current” and “Factory” numbers are expressed in milliampere-hours (mAh). There is a very technical explanation of what this is over at Wikipedia, but essentially the higher the number the longer a battery will last.
Current Capacity: Shows the current maximum capacity of the battery.
Factory Capacity: Shows the maximum capacity of the battery when it left the factory.
Percent of Original: Shows your battery’s current maximum capacity expressed as a percentage of the maximum capacity when it left the factory. Apple says that for a properly treated battery that this number should remain at 80% or higher at least until the current number of load cycles reaches the factory load cycle count.