Synergy.

Synergy is when two different industry's come together to promote one another and is when both parties benefit from the two joining together. Synergy within the music industry is when a song is used to promote many number of things which range from promoting movies to businesses. This is used as it is a very successful way of gaining more audience if a song is created for a movie this is because people who love that artist see them create a song for this film which makes them very loyal fans want to go see the movie. 

A prime example for this is Adele. Adele created the song 'Skyfall' for the newest James Bond movie 'Skyfall'. Adele is a very big artist so getting her to write a song for this movie helps promote the movie to Adele's large fan base which then people apart of her fan base who was not a fan of previous James Bond movies may go and see the new one as one of their idols created the soundtrack for it. Also Adele benefits from this as many people who watch James Bond may not have heard Adele and listening to the soundtrack may entice them to go listen to Adele's music helping her gain more fans. 

Another example of this is Justin Timberlake song  'I'm Lovin' it' this song was created to promote McDonalds as it uses there theme tune within the song this again is similar to the Adele situation where both parties benefit from getting their product out to people who may not have come across them before which brings them more fans/customers.