The Skydome HDRI-brand is a collection of high-dynamic range images, which displays only the sky-portion of an outdoor setting. Usually the qualities selected under the brand are cloudy and detailed skies. The lighting-condition is natural exterior lighting, with no artificial sources, and captures all spheres of natural lighting.
Few sunset clouds captured in high detail for image based lighting. Only top half of the HDRI-sphere is shot, so if using for example VrayLight with Dome-setting enabled, leave the “Spherical: full-dome” unchecked.
6104×1532 panorama, 4240×2832 backplates
Panoramic JPEG-image, JPEG backplates and TIFF RAW backplates for better compositing options.
Samyang 24mm f1.4
It might be confused as to what in actuality the HDR-images are used. They are used in variety of 3D-formats to produce physically accurate lighting (to recreate the lighting conditions present in the scene which from the panorama was shot), for variety of purposes. I could say the most common usage is for achieveving lifelike light conditions to architectural renders, but also for your fantastic 3D-scenes where you want to breathe a bit of life into the images, to bring them from merely ordinary 3D-renders to the hyperrealm domain.
About HDRI in general:
About the usage of HDRI in 3DS Max and VRay: