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1.
1. something sold because something else is sold

2. a connection
Unfortunately, it seems like every game that is availible for rent at blockbuster is a movie tie-in.
by The Return Of Light Joker November 06, 2007
 
2.
(n.) Product pertaining to a popular media culture or icon.
The tie-ins (such as videogames, toys, cartoons) to the batman movies, 60's series and comics were worth several times the amount of the actual product.
by Kung-Fu Jesus May 07, 2004