1. Discharge that takes place while the battery is in an open-circuit condition.
2. The rate at which a battery, without a load, will lose its charge. This can vary considerably depending on the type of battery and age. It can be as low as 3% a month for a new AGM battery, and as high as 10% a week for an older Lead-Antimony (industrial) battery.
http://www.arts-energy.com/glossary/ (1.); https://www.solar-electric.com/learning-center/general-solar-information/photovoltaic-solar-power-glossary.html (2.)
Author: Thomas D.