OGC Web Coverage Service (WCS)
Like the OGC WFS allows a client to access vector datasets, the OGC Web Coverage Service (WCS) allows a client to access raster datasets. By rasters we mean data that are represented as a matrix of cells in continuous space organized in rows and columns where each cells contains a value. Thus WCS service provide access to different types of gridded data such as Digital Elevation Model (DEM), remote sensing imagery, etc... It must be noted that WCS gives only access to the raw data and does not have transactional capabilities.
OGC Web Coverage Service specification: http://www.opengeospatial.org/standards/wcs