Any type of musical chord that gives an ominous, yet grand sound to audibly describe the vastness or wonders of space. Many examples can be found in common Sci-Fi films, usually during scenes of open, empty space. Space chords can also be created accidentally or be unintended in a situation.
John: Can you help me with these chord progressions on my keyboard?
Ben: Wow dude, that last chord you made sounded like a space chord.