Why are some episodes marked as "Specials"?

A special episode is an episode that is linked to a show but is not necessarily part of the show's storyline and is therefore not required viewing. It can, however, be interesting, sometimes to better understand a season finale, etc.

Special episodes on BetaSeries are preceded by an "S" icon; you can be at 100% on a show by watching them or by hiding them, but they only add to your time spent in front of the TV if you mark them as watched.

If you do not want to see them at all, you can disable their display in your account settings.

Like other episodes, you can also hide them directly from the Episodes to watch view or from the relevant episode's page: How to hide episodes from my to-watch list?