Bollywood (Hindi: बॉलीवुड, Urdu: بالیوڈ, Punjabi: ਬੋਲੀਵੁਦ‌) is the informal name given to the popular Mumbai-based Hindi language film industry in India. The term is sometimes used incorrectly to refer to the whole of Indian cinema.

The name is a blend of Bombay, the former name for Mumbai, and Hollywood, the center of the American film industry. Though some purists deplore the name, arguing that it makes the industry look like a poor cousin to Hollywood, it seems likely to persist and now has its own entry in the Oxford English Dictionary. Such names have also been used for other industries, including Kollywood, Tollywood, Lollywood, Dallywood, and Nollywood.

Bollywood and the other major cinematic hubs (Tamil, Marathi, Bengali, Telugu, Malayalam, and Kannada) constitute the broader Indian film industry, whose output is the largest in the world in terms of number of films produced and in number of tickets sold. Bollywood is a strong part of popular culture of not only India, but also of the rest of South Asia, the Middle East, parts of Africa, parts of Southeast Asia, and among the South Asian diaspora worldwide. Bollywood has its largest diasporic audiences in the UK, Canada, Australia and the U.S, all of which have large Indian immigrant populations.

Bollywood is also commonly referred to as "Hindi cinema", even though Hindustani, the substratum common to both Hindi and Urdu, might be more accurate. The use of poetic Urdu words is fairly common. The connection between Hindi, Urdu, and Hindustani is an extremely contentious matter and is discussed at length in the linked articles relating specifically to the languages.

There has been a growing presence of English in dialogue and songs as well. It is not uncommon to see movies which feature dialogue with English words and phrases, even whole sentences. A few movies are also made in two or even three languages (either using subtitles, or several soundtracks).

Bollywood film music is called filmi music (from Hindi, meaning "of films").

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. While most actors, especially today, are excellent dancers, few are also singers. One notable exception was Kishore Kumar, who starred in several major films in the 1950s while also having a stellar career as a playback singer. K. L. Saigal, Suraiyya, and Noor Jehan were also known as both singers and actors. Some actors in the last thirty years have sung one or more songs themselves; for a list, see Singing actors and actresses in Indian cinema.

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. One of the most recorded of these playback singers is Lata Mangeshkar who, through the course of a career spanning over six decades, has recorded thousands of songs for Indian movies. Many of the female songs in films from the 1950s, 1960s, and 1970s were sung by Lata or by her sister Asha Bhosle. Some of the famous male playback singers were Mohammed Rafi, Mukesh, and Kishore Kumar. The composers of film music, known as music directors, are also well-known. Their songs can make or break a film and usually do. Remixing of filmi songs with modern beats and rhythms is a common occurrence today, and producers may even release remixed versions of some of their films' songs along with the films' regular soundtrack albums.

The dancing in Bollywood films, especially older ones, is primarily modelled on Indian dance: classical dance styles, dances of historic northern Indian courtesans (tawaif), or folk dances. In modern films, Indian dance elements often blend with Western dance styles (as seen on MTV or in Broadway musicals), though it is not unusual to see Western pop and pure classical dance numbers side by side in the same film. The hero or heroine will often perform with a troupe of supporting dancers. Many song-and-dance routines in Indian films feature unrealistically instantaneous shifts of location and/or changes of costume between verses of a song. If the hero and heroine dance and sing a pas-de-deux (a dance and ballet term, meaning "dance of two"), it is often staged in beautiful natural surroundings or architecturally grand settings. This staging is referred to as a "picturisation".

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.

Bollywood films have always used what are now called "item numbers". A physically attractive female character (the "item girl"), often completely unrelated to the main cast and plot of the film, performs a catchy song and dance number in the film. In older films, the "item number" may be performed by a courtesan (tawaif) dancing for a rich client or as part of a cabaret show. The dancer Helen was famous for her cabaret numbers. In modern films, item numbers may be inserted as discotheque sequences, dancing at celebrations, or as stage shows.

For the last few decades Bollywood producers have been releasing the film's soundtrack, as tapes or CDs, before the main movie release, hoping that the music will pull audiences into the cinema later. Oftentimes, the soundtrack is more popular than the movie. In the last few years some producers have also been releasing music videos, usually featuring a song from the film. However, some promotional videos feature a song which is not included in the movie.