What is per title encoding?

I saw the per-title-encoding option in Gumlet while processing a video, can anyone tell me what exactly it is?

Gumlet uses per-title-encoding to determine the lowest possible bitrate for a video by analyzing the material, maintaining the visual quality of the original video, and minimizing the size of the transcoded video.
For example:

Original Video:

Gumlet Per-title-encoded Video:

As you can see in the above movies, the original video is 151 MB and the per-title encoded video is 104 MB, so per-title-encoding allows us to accomplish a 47 percent reduction in size while maintaining the same visual quality.

Here is the detailed article on this topic: The power of per-title encoding

And this is how it works: