Audio and video files, as well as other data streams can be encoded and decoded using a certain codec. Files are typically encoded in order to transmit or save them in a secure way. Thus, in order to view or play the file or stream, the same codec is needed for decoding.
These codecs, of course, have names. While most codecs are known by some abbreviation of the name, the Codec Long Name gives the full name of the codec in question. For example:
If the Codec Long Name is present in a file, it automatically means that the file is encoded.