Technically it is only form factor. The common CR2032 coin cell uses the same number system. The first 2 digits are the diameter in millimeters, the remaining

Technically it is only form factor. The common CR2032 coin cell uses the same number system. The first 2 digits are the diameter in millimeters, the remaining digits are the height in tenths of milimeters. So a CR2032 is 20mm across and 3.2mm tall. The "CR" portion is what indicates the battery chemistry. The correct IEC notation for would be ICR18/650 where the first two letters specify the specific anode and cathode material (I've picked the letters most commonly seen in examples). Those letters are absolutely critical in determining the nominal voltage, because without them, we could even be describing say an alkaline disposable cell of the same shape (LR18/650 would be such an non-rechargeable alkaline battery of the same shape).