Map usually reffers to a .map file which contains a complete level built out of sectors and sprites. The format is documented at the end of the text displayed by buildhlp.exe from the duke cd and in the file buildinf.txt in src.zip in http://www.advsys.net/ken/buildsrc/kenbuild.zip .
Map can also reffer to the overhead map shown when tab is pressed. On the first press the map is shown as a transparent overlay on the second press it is shown with solid fill for the floors. On the third press the display returns to normal.
note: in current public releases the solid map mode is broken. This has already been fixed in internal development versions.