Dynamic Range

The ratio between the largest and smallest measurable value is called the dynamic range.  Those with an engineering bent often express dynamic range in decibels (db):

where the two readings being compared are in volts.  It is also convenient to use the resolution of the associated analog-to-digital electronics.  Thus, you may see dynamic range expressed in bits (e.g. 16 or 20 bits).  

Useful wide dynamic range requires more than extra bits -- high-quality, low-noise electronics are also needed to ensure that any extra bit depth is well used.