The duration of a task after it has been padded with a safety factor, typically to an estimate in which you have about a 90% confidence of meeting.
When estimating duration for a Critical Chain project, it is common to incorporate two different estimates into your schedule. The estimate you work with on a daily basis for planning and tracking purposes is the one entered into the Duration Task field. Typically you should have about a 50% confidence level in this estimate. The other estimate, Safe Duration, is the one that is padded with enough buffer to safely share with people outside the project, who may need to plan their activities based on your ability to meet your schedule.