ADIF is a computer file data specification which allows different computer logging programs to share data between each other. The ADIF country codes have no usefulness except to computer programmers.
The ARRL countries list, as well as this larger compedium of info found at:http://www.ac6v.com/opaids.htm
Prefix Entity Cont. ITU CQ
DA-DR(14)* Fed. Rep. of Germany EU 28 14
The Prefix column is the range of prefixes (that part of a call before the number) that can be used by the Entity or country. So in the above example, if you hear a DA3 or a DB3 or a DC3 all the way to DR3 (or other numbers), then you will be talking with the Fed Rep of Germany. All countries divide themselves into the numbers, like we do here in the US.
The Cont column is the Continent. Germany is on the EU or European continent. There is a Worked all Continents award and this info is useful to those award hunters.
The ITU column is the unique ITU designation for that country; there may be a Worked all ITU award but I'm not sure.
The CQ column is the designation of the CQ zone for the country. CQ Magazine has divided the world into a bunch of zones and folks use these for the Worked all Zones award. This is also the zone part of the exchange that you give out if you're in any CQ sponsored contest.
Does this help?