Image version
Garmin map image is standard version for all Garmin devices and software solutions for other mobile devices. File extension is always .img, path and file name depends on device and function of the image, look >>>here.
[color="#FF0000"]NOTE: Garmin *.img files are no CD/DVD images! They are not compatible with well known image burning programs![/color]

MapSource, CD/DVD, PC or gmap version
These are all names for map versions, which has to be installed on PC or Mac, e.g. for route planning and trip evaluation and for arrangement of individual mapsets for GPS devices.
For many years the Windows program Garmin MapSource was standard for this task, thats why the notation MapSource version is very common, although MapSource is developed since 2010 no more. Today the programs Garmin BaseCamp, HomePort and MapInstall have taken over this job.
Some years ago Garmin changes the format from classic MapSource to gmap format (so called, because the map folder has extension .gmap). The gmap format is Mac compatible and both formats are fully convertible.

[color="#FF0000"]NOTE: With MapSource/gmap version of a map you can create a fully functional Image version with MapSource or MapInstall, but from Image version you never can extract a real MapSource or gmap version![/color]

locked or unlocked
Original Garmin maps and maps of commercial third party supplier are locked. That means they are protected by special code for exclusively usage on one device or by one user. But it is possible to remove this code so that this map can be used on every device by every user. That means unlocked.
Today it is very easy to unlock a map with unlockers from our Software section.

City Navigator
So Garmin calls its normal routable street maps.

cityXplorer
Garmin map series of city maps, that contains data for routing with public transport. They work with current nuvi series like nuvi 1xxx, 2xxx and 3xxx. For all other devices this maps are only small pieces of City Navigator maps.

NT
...could stand for NaviTotal :D, but in connection with Garmin maps it mostly signifies New Technology. It is a compression procedure to make maps smaller. All Garmin devices and softwares about from 2005 supports this technology. Only some really old devices can't read NT maps (e.g. StreetPilot III, Quest , ...).
[color="#FF0000"]NOTE: There is no known method to convert NT maps to nonNT and reverse![/color]

Unicode
Current City Navigator Europe maps are available as [I]NT as well as NTU (Unicode) maps. The Unicode version includes codepage 65001 for special characters of eastern european languages and cyrillic script. Normal NT version only has western european characters. Only current Garmin unit series (about from 2010) can use Unicode versions. All other devices can't show cp 65001 characters.