The term zone, as applied to reservoirs, is used to describe a unique interval which has one or more distinguishing characteristics, such as lithology, porosity, saturation, etc. (ITOGP)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}