Bollywood is the name given to the popular Mumbai-based Hindi language film industry in India. The name is a play on the words Bombay (former name for Mumbai) and Hollywood, the US film industry centre.
Bollywood music or filmi (from Hindi, meaning “of films”) is an essential element of the movies. A Bollywood movie without songs and dances would need to be particularly strong in other departments to avoid being considered a rip-off by the Indian audience!
Songs from Bollywood movies are generally pre-recorded by professional playback singers, with the actors then lip synching the words to the song on-screen, often while dancing – few actors actually sing. Playback singers are prominently featured in the opening credits and have their own fans who will go to an otherwise lacklustre movie just to hear their favourites. Their songs can often make or break a film.
Songs typically comment on the action taking place in the movie, in several ways. Sometimes, a song is worked into the plot, so that a character has a reason to sing; other times, a song is an externalization of a character’s thoughts, or presages an event that has not occurred yet in the plot of the movie. In this case, the event is almost always two characters’ falling in love.
Remixing of filmi songs with modern beats and rhythms is a common occurrence today, producing a beautiful blend of the modern with the traditional.
– Extract from Wikipedia