For example, you can be In a beautiful village surrounded by greenery and blue sky, which has 360° panorama view.

In an HDRI Backdrop mode, you are actually in a huge dome to which a high dynamic range image is applied.

HDRI Lighting is technically called 'image-based lighting'.  With the HDRI Backdrop mode, the Image-based lighting surrounds the scene and provides HDR illumination, HDR reflections, and a HDR background.

Most HDRIs are captured photographically at a real location. Think of the HDRI not as a photographic image, but as an accurate measurement of the brightness and color of the light coming from all directions around the camera. Each pixel on the flat HDR image stores a color and brightness value for a specific direction and this will be mapped onto the environment lights surface.