To give the effect or appearance of being from the past, specifically the 1980's, to any work of art, music, or video game.
Retrostylization is becoming a popular style used in art, media, and advertising, as the children of that particular era are becoming adults.
This term was coined by Paul Hubans to describe his game, MADHOUSE.
Wow man, have you played MADHOUSE? It was made in 2004 but it has retrostylized graphics to give the appearance of looking just like a Nintendo game! Sweet!