A hole or shaft constructed in the earth intended to be used to locate, sample, or develop groundwater, oil, gas, or some other subsurface material. The diameter of a well is typically much smaller than the depth. Wells are also used to artificially recharge groundwater or to pressurize oil and gas production zones. Specific kinds of wells should be specified in the SamplingFeature description. For example, underground waste-disposal wells should be classified as waste injection wells.
The term is from OGC Observations and Measurements (see https://www.seegrid.csiro.au/wiki/AppSchemas/ObservationsAndSampling#Sampling_model), but the definition is from the USGS SiteTypes http://wdr.water.usgs.gov/nwisgmap/help/sitetype.html.