"Reservoir" carries distinct technical meanings across disciplines — all sharing the core concept of storage and supply.
A natural subsurface formation of porous, permeable rock (sandstone, limestone, fractured granite) that stores and transmits groundwater or hydrocarbons. Characterized by porosity (storage capacity) and permeability (flow capacity). Example: "The Ogallala Aquifer is a vast freshwater reservoir underlying the Great Plains."
An artificial storage facility for liquids or gases: water supply reservoirs (dammed valleys), tank farms (petroleum, chemicals), gas holders, pressure vessels. Designed for capacity, safety, controlled release. Example: "The tanker loaded at the coastal oil reservoir terminal."
A source or reserve supply of anything valuable — knowledge, talent, patience, capital, goodwill. Implies depth, accessibility, and replenishment potential. Example: "She drew on a deep reservoir of institutional memory."
A buffered storage area in memory (RAM) or database for temporary data holding during processing. Reservoir sampling (algorithm for random sampling from streams). Example: "The frame buffer reservoir smooths video playback during network jitter."
Input → Storage (with retention) → Controlled Output. Whether water in sandstone, oil in tanks, wisdom in experience, or packets in RAM — a reservoir mediates between supply variability and demand continuity.