This is a {{spoiler box}}
with the title "Behind the scenes information", allowing the editor of a page to hide production notes (or Doylist "out of universe" information) from casual viewers.
It puts the text inside a box that can be expanded with a "show" button.
Usage:
{{OOU box|hello world}}
{{OOU box|1=E=mc<sup>2</sup>}}
1=
before it.For stronger hiding, put the text on the article's talk page.