360 Degree Video is an immersive video format consisting of a video – or series of images – mapped to a portion of a sphere that allows viewing in multiple directions from a fixed central point.
The mapping is usually carried out using equirectangular projection, where the horizontal coordinate is simply longitude, and the vertical coordinate is simply latitude, with no transformation or scaling applied. Other possible projections are Cube Map (that uses the six faces of a cube as the map shape), Equi-Angular Cubemap – EAC (detailed by Google in 2017 to distribute pixels as evenly as possible across the sphere so that the density of information is consistent, regardless of which direction the viewer is looking), and Pyramid (defined by Facebook in 2016).
This type of video content is typically viewable through a head-mounted display, mobile device, or personal computer and allows for three degrees of freedom (see section 4.2 for an explanation of the concept of degrees of freedom).