A station composite is typically an edited combination of any/all facets to your radio station. Think of it like an aircheck for a PD. Instead of putting the best breaks from one jock (you), you put the best breaks from the entire station, regardless of the jock. Mix in imaging or anything that helps define the character of the radio station. Use the station composite to showcase the best content your station has previous had to offer.
The idea is to compel the person listening in the shortest time possible.