What is a music video?

A music video or song video is a short film integrating a song and imagery, produced for promotional or artistic purposes, modern music videos are primarily made and used as a marketing device intended to promote the sale of music recordings. There are also cases where songs are used in tie in marketing campaigns that allow them to become more than just a song.
1894 saught the first image based video, sheet music publishers Edward B. Marks and Joe Stern hired electrician George Thomas and various performers to promote sales of their song "The Little Lost Child". Using a magic lantern, Thomas projected a series of still images on a screen simultaneous to live performances. This would become a popular form of entertainment known as the illustrated song, the first step toward music video.
Music video's have increased in popularity through the years boosting artist recognition also sometimes including a narrative or explicit stuff which have been seen as controversial.
Often video's are used to help promote a product, sometimes clothing brands are used a lot or are worn, this then engages with that artists audience. Music video's are a source for revenue, big companies like Sony who have artists signed to their company usually have directed videos.
There are a number of key features of a music video, Andrew Goodwin identified six key features:

1. Music videos demonstrate genre characteristics (dance routine for boy/girl band)
2. There is a relationship between lyrics and visuals (illustrative, amplifying, contradicting)
3. There is a relationship between music and visuals (illustrative, amplifying, contradicting)
4. The demands of the record label will include the need for lots of close-ups of the artist may develop motifs which recur across their work (visual style)
5. There is frequently reference to the notion of looking (telescopes) and particularly voyeuristic treatment of the female body.
6. There is often intertextual references (tv programmes, films, brands etc)

Also good to consider whether the video is primarily performance based, narrative based or concept based and how elements of each are used in it.