What is a map service?
The map service is the way that you publish maps to the Web using ArcGIS. You'll make the map in ArcMap, then publish the map service to ArcGIS Server. Internet or intranet users can then use the map service in Web applications, ArcMap, ArcGIS Explorer, and other applications.
A map service makes maps, features, and attribute data available inside many types of client applications. ESRI provides .NET, Java, SOAP, and REST interfaces for working with map services. One common use of a map service is to show business data on top of base map tiles from ArcGIS Online, Bing Maps, or Google Maps.
Additionally, when you publish the map service you can choose to expose it through the KML or OGC WMS specifications. This can make your map service available to a broader variety of clients, such as Google Earth.
All map services begin inside ArcMap where you create your map. When you've finished the map and are ready to publish it, open the Map Service Publishing Toolbar. The items on the toolbar help you publish your map as a service. See Publishing a map service for full instructions.