The term Bollywood was created by conflating the city Bombay (now known as Mumbai).
Bollywood is not a name for the Indian filmmaking industry; it is a name for the country's Hindi film industry. Films are made in various other languages in India, and each language's industry carries its own name (such as "Tollywood" and "Kollywood").
Basic Content/ Structure
There is alot of content in Bollywood films they tend to have a lot of drama, it also contains catchy music in the form of songs with dances. There are over 100 background dancers been choreographed in the dance sequences. Bollywood movies have songs and dances because that's an integral part of the indian culture. The music from the films is released before the movie; this can often help increase the audience views for the film.
The use of language in Bollywood films is mainly Hindi which is also the national language of India. However contemporary mainstream movies also make great use of English.
Music in Indian cinema is a substantial revenue generator, with the music rights alone accounting for 4–5% of the net revenues generated by a film in India.The major film music companies of India are Saregama, Sony Music etc. Commercially, film music accounts for 48% India's net music sales. A typical Indian film may have around 5–6 choreographed songs spread throughout the film's length. 
"Cinema of India" [Accessed 09 December 2014]