A premiere is the first official screening of the newly opening movie. Usually this event is vastly more luxurious than the rest of the screenings, a gala where the director, actors, producers, the rest of the people to blame for the movie and perharps other special guests somehow related to the movie also come.

Also name of Adobe's excellent digital video editing software (Adobe Premiere)

This definition probably bears some resemblance to iMDB's definition...