A frequently untranslated Japanese word in video game titles (such as Ninja Gaiden) and other media. Has been translated as "side story" (example: Gundam: Side Story), "foreign telegram", "message from beyond".

The feeling I get from this word (not being a fluent in Japanese) is of a story taking place in a sort of a alternate reality, often when a game series has an established timeline of events and another game is published which does not fit with the timeline.

Gai (外) - According to my dictionary translates roughly to "outside". Also used in the word gaijin.

Den (伝) - Roughly translates to "transmit", or "impart". Also occurs in the word denki (biography), and densetsu.