Answer:
Free slack.
Explanation:
In project management, free slack refers to the amount of time that a certain task can be delayed and not affect the completion time of the general project. Slack time can be considered "just in case" time, because even though delays should be minimized, rarely you can eliminate them completely, and slack time gives you a little extra room for managing projects.
In this case, the free slack time is 10 days, and this delay will consume 9 of them.