Retrospective meetings contain categorized ideas. The holding bin is a special category on the board that is used to hold ideas that are uncategorized. While we don't allow users to create uncategorized ideas directly in Instant Agenda, ideas can become uncategorized in a variety of ways.
When you apply a category template in a Retrospective meeting, the categories you currently have on the board are replaced with the new categories. But if your attendees have already started submitting ideas, the categories those ideas were associated to no longer exist. So, the holding bin is where all those ideas will be placed in the interim.
Integrations are another way in which ideas can be added to the holding bin. When ideas are created from an integration, they are uncategorized by default so they are placed in the holding bin waiting for you to categorize them.
The holding bin is not intended to be used as category of ideas during your retrospective, but rather as a temporary coral. You can not group ideas in the holding bin, nor can they be voted on or discussed during the Insights and Actions step. If your retrospective board contains ideas in the holding bin, it's a good practice to either move those ideas into an existing category, or delete them from the board before starting your retrospective.