Nintendo DS files are often named after their magics. A few characters in the magic help name our common file types. Not all of these names are confirmed.
N - Nitro - Name used to describe the Nintendo DS. Usually the first (or last) letter.
R - Resource - Used commonly with image formats. Usually the last (or first) letter.
C - Compressed - Usually replaces the first (or last) letter of another format to indicate a compressed file.
Alpha Naming System
Here at Project Pokemon, we accept formats to be read as either forward or backward as long as they don't have different meanings. The derivation is due to different parsing of the magic. It can either be interpreted as a string, or a UInt32. NARC is the string version of a NARC (official) file. CRAN is the UInt32 version. RECN is the string of the NECR (official). NECR is the UInt32 of the same file. The most official is via UInt32's, however instances like NARC, string is also accepted.