An instrument definitions file i.e. Korg M1.ins or Roland JV1080.ins or AD2.ins can hold all the bank and patch names for an instrument. This information can then be used by SONAR for selecting different banks and patches.
Most drum software's tend not to banks and patches, kits yes but you tend to select your kit at the start of a project and not change it through the life of the project.
A drum map, maps a particular MIDI Note to another MIDI note, i.e. you could Map MIDI note 65 to MIDI note 22, sounds daft but for if you have a MIDI drum controller that has fixed MIDI note for each pad or pad then it is useful.
e.g. You drum controllers snare out puts MIDI note 100 and can not be changed but your drum software expects the snare to be on MIDI note 32 you can use a drum map to map note 100 to note 32.
Or in your case Billy86 map a keyboard controller key to a drum in AD2, or SD2 or any other drum sound source.
Drum maps can also be useful in other circumstances not just drums.