See https://wiki.factorio.com/Types/EntityP ... 2hidden.22wiki[/url wrote:Hides the entity from the bonus GUI (button above the map) and from the made in property of recipe tooltips.
But as Rseding91 confirmed here 89383 in also makes the entity immune to selection tools just like the flag "not-blueprintable". I made a modding interface requests here 89397 to change that, or at least give another option.
(A few other flags also have no explanation, but I don't know if they would be even necessary to a more experienced modder than me.)