What's the unplanned cost that's displayed on the Manage Budget Versions page?

The cost that's incurred on the project for a resource that's not planned in the budget version. Unplanned cost is equal to the sum of unplanned inception-to-date actual and committed cost.

Let's say you created a baselined budget version with budget lines for Alex and Emily. Now, $100 is incurred on the project by John who wasn’t initially planned in the budget version. So, $100 is displayed as the unplanned cost on the Manage Budget Versions page. Later, when you plan for John in the budget version, a check mark is displayed indicating that there are no unplanned costs for the budget.