Open Geospatial Consortium, Inc. (OGC) — An organization comprising companies, government agencies, and universities that defines specifications for providers of geospatial data and developers of software designed to access that data. The specifications ensure that providers and clients can talk to each other and thus promote the sharing of geospatial data worldwide. You can access the Web Map Server Implementation Specification at the OGC website.

Web Map Service — The OGC^® defines a Web Map Service (WMS) as an entity that "produces maps of spatially referenced data dynamically from geographic information."

WMS server— A server that follows the guidelines of the OGC to render maps and return them to clients.

georeferenced — Tied to a specific location on the Earth.

raster data — Data represented as a matrix in which each element corresponds to a specific rectangular or quadrangular geographic area.

map — The OGC defines a map as "a portrayal of geographic information as a digital image file suitable for display on a computer screen."

raster map — Geographically referenced information stored as a regular array of cells.

layer — A data set containing a specific type of geographic information. Information can include temperature, elevation, weather, orthoimagery, boundaries, demographics, topography, transportation, environmental measurements, or various data from satellites.

capabilities document — An XML document containing metadata describing the geographic content offered by a server.