Definition: Hydrology, a scientific discipline concerned with the study of water, its sources and flow through bodies of land or water, and how these processes change over time. It includes both natural and anthropogenic hydrological systems such as rivers, lakes, oceans, and wetlands. The term "hydro" refers to water itself, while "lithology" describes rock formations. The word "hydrology" is derived from the Latin word "hydro-", meaning "water," and is related to water quality, which includes the amount of dissolved substances in the water, its chemical composition, and the quantity of pollutants it contains. The term "hydrol" is often used interchangeably with "hydrology" but carries a different connotation. Hydrol refers to the process by which water moves through an area, whereas hydrology typically focuses on the physical processes that occur in water bodies, such as their flow and movement. Both terms are essential components of understanding water cycle and its relationship to the Earth's system.