WMS (short for Watershed Modeling System) is a hydrology software used to create and analyze models of water quantity and quality in natural systems like rivers, lakes, and groundwater aquifers. It allows users to input data such as topography, land use, and precipitation, and then simulate the flow of water and the movement of contaminants through the system. Its ability to dynamically link data from different sources makes it a powerful tool for hydrologic analysis and management.