Web map server
A web map server (WMS) is a web application which provides portrayal of geographic data which is stored on the server. This data can be stored in a variety of data formats but is served in a limited number of image formats.
This provides the useful ability to restrict access to data since only a picture of the data is sent to the user and the high quality vector or raster data remains safe on the server. This is in sharp contrast to a Web Feature Server (WFS) which returns the features of the data as features.
The Open GIS Consortium publishes a specification for web map servers [1].