Once you start having a lot of cards, and you have multiple members contributing to a parent card, some information may not seem relevant to you. Or you might have added a card to multiple parents. Orrr you may have some cards you don't want people to see when viewing your notes in public.
How to Hide
Hiding is personal, so you don't have to worry about affecting anyone else if you have shared your card. You can only hide cards if they are within a parent. To hide, either click the parent-child relationshop indicator (the circle) under the card title and then click 'Hide'. And it is as simple as that!
The 'Hidden' filter is on (inclusive) by default, but you can enable/disable it in the Filters Panel.