What is Keeping?
As soon as you create, join or interact with a card, it's yours to Keep. If you do any of the following a card is automatically 'Kept':
Adding the card to a parent
Adding a tag
Adding a child card
Notice that Commenting is excluded - so you can offer advice and help even if the Card might not be directly relevant to you.
You can see if you have 'kept' a card, by looking at the more actions panels, like so:
All the Cards you have 'Kept' will be available in your Home, even if they get cut from the original parent card you found them in or if your permissions change. The number of cards you have 'Kept' is equivalent to the number of cards contributing towards your 'card count'. You cannot 'Unkeep' a card, however you may 'Junk' it and it will no longer contribute towards your card count.