Map tiles are portions of a map that are seamlessly joined on the fly while you are panning and zooming in the map window. Each pan and zoom is a call to the server to request the appropriate map tile(s). Only those that fit the bounds of the map view and match the zoom level are returned. Google Maps and Bing Maps are examples of applications that use map tiles.
Map tiles are created by dividing a map into levels that represents specific zoom levels. Level 0 is the entire map, Level 1 is one level zoomed out from the entire map and divided evenly into four tiles. Level 2 contains 16 tiles, which are the four tiles from Level 1 divided evenly. Level 3 are the 16 Level 2 tiles subdivided into 64 tiles. Levels 0-3 of a world map typically show global levels detail, while higher levels, are zoomed in to show street-level detail. Actual zoom levels are dependent on the bounds of the named map.
At very high levels (16 and above), the number of tiles is huge. For faster retrieval, you can pre-render the tiles if you know the map layers will not change. Or for more dynamic map tiles, you can cache them and provide an expiration date so that new tiles are generated when necessary.