The resolution. This indicates Full HD quality (1920x1080 pixels).

If you are trying to understand what the string of characters means, Season 1, Episode 1.

In the early days of the internet, files were often named vaguely, leading to "fakes" or poor-quality downloads. The adoption of this "Scene Standard" naming convention (Title + Year + Source + Resolution + Codec + Group) transformed the way digital media is organized.