Unreal Engine is a Real-Time rendering program. This means that every scene is rendered on the go, for example at 60 frames per second. Rendering programs like Blender or Maya, however, focus on rendering near-perfect images one by one. In these cases it can take hours to just render one frame.
And that’s exactly where Unreal Engine is shining. It is able to render scenes at an incredible speed and an incredible quality. While this fast rendering requires cutting corners, Unreal Engine is able to visualise the scenes in acute detail and mirror reality.
Compared to other Real-time engines, Unreal Engine has the ability to build very life-like environments with the smallest amount of work. Other engines tend to focus more on performance (still also very important), and require the 3D artist to build up the scene from a low-quality to a high-quality scene. In Unreal Engine you typically work the other way around: you start from something medium quality and work your way up or down depending on the requirements.