Definition:
Bodystorming is a technique which is an improvisation of brainstorm based on interaction and movement of body. The idea is to imagine the product exists and act as though it would be used. It is experiencing virtually the product which is an idea through an improvised artefacts and physical activities envision a solution. The idea behind this is to get people up and moving, trying things out with own body, rather sitting around a table and just discussing with the abstract idea.
This is a User Experience Design (UXD) technique a proper user-centered method carried out by the designers as well as the users of the the final product. Ideal to design physical spaces used to design physical products and software. Bodystorming should be one of the first steps taken in the problem definition stage .
Further Reading:
https://en.wikipedia.org/wiki/Bodystorming
https://methods.18f.gov/discover/bodystorming