The Unreal Engine is a game engine made by Epic Games, a major game studio that is known to have created titles such as Infinite Blade, Fortnite, Rocket League. While perhaps more well known by their games in the general public, the Unreal Engine itself is perhaps the most powerful creative tool invented by Epic.
With many other game engines out there such as Unity, Godot Engine, Love, etc, Unreal is the most well known for its out-of-the-box graphics qualities. Without much customizations, creators are able to create realistic worlds using the physics based rendering engine inside of Unreal. With the recent preview of Unreal Engine 5, the graphics has only gotten better.
That side, the power Unreal Engine enabled the developers and designers alike is the ability for them to quite literally realize the impossible and bring alive from industrial rendering to fantastic worlds that are distance. Real-world architects and fantastic game developers alike are able to use the tools to their own needs.