Web Map Service — an Open Geospatial Consortium (OGC) standard protocol for serving georeferenced map images over the internet.
A WMS server renders geographic data as image tiles (PNG, JPEG) and delivers them to a client application. The client specifies the geographic extent, image size, coordinate system, and layers it wants, and the server returns a rendered image. WMS is widely used for background map layers and reference data.
Unlike WFS, which delivers raw geographic data, WMS delivers pre-rendered images. This makes WMS faster for display but unsuitable for analysis — you cannot query individual features from a WMS image.
Example: Natural Resources Canada provides a WMS service for topographic maps. A GIS application can add this WMS as a background layer, displaying the topo map behind other data layers without downloading the full dataset.