Stock Footage.

Stock Footage.

Stock footage is pre-shot footage from a different filmmaker and is used as a way to save money on shooting specific scenes. Stock footage can also be used as story developing device and can build tension within the audience. It tends to be historical either footage, outtakes or simply footage that never got used.
There are numerous websites available to obtain stock footage including
http://www.stockfootageonline.com/
http://www.stockfootageforfree.com/

http://www.bbcmotiongallery.com/
The video below is a example of stock footage.