Rendering engine usually happens to be something like an “add-on” to the 3D software that helps compute the lighting and physical properties of the materials used in a more photorealistic way than the default renderer that comes with a given 3D software. Common rendering engines are Corona renderer, Vray, Redshift, Fstorm, Lumion, Octane or Cycles (proprietary of Blender).

There are two types of renderers: raytracing ones (mentioned above) that utilize actual calculations of lightrays hitting the surfaces and adjusting the look of the image based on physical properties of the materials (such as diffuse, bump, displacement, roughness etc.) and the other group – real time rendering engines such as Unreal Engine, Eevee in Blender or Unity.

Those are most commonly found in game industry and rely primarily on quick approximations of shadows, pre-set (baked-in) lighting and other memory-saving procedures.