A private card is one that only you can see, edit, or delete. A private card will be a part of your Info Library Record, but not your co-parent's Record.
A shared card is available to both you and your co-parent. Only the parent who created the card has the ability to change or delete it. Both co-parents can see the card in their account and on the Info Library Record.
Please note: Sharing a card does not create a new tab for your co-parent, but it will show the name of the tab in which your card is located. Sharing a single card within a tab does not share other private cards.
*If a card has been shared at any time, the information in the card at the time it was shared is permanently available on your co-parent's Info Library Record.