Web Coverage Service (WCS) publishes raster-based layers. The Geo ArcGrid includes a couple of geospatial example of coverages. It's almost like having both WMS and WFS in one service. It allows clients to get raster data along with geospatial data to make more analysis locally.
A detailed description of WFS and WCS are out of the book's scope; Chapter 12, Going Further - Getting Help and Troubleshooting, will give you a brief view of both. You will learn how to perform basic requests.