Active

This field can be used to indicate whether a task is active on not.  Inactive tasks will not appear in a users timesheet or expense report for charging against.

Note: there is an exception -- if a task was used on a timesheet or expense report and subsequently changed to inactive, users will still be able to charge to that task for the duration of that timesheet or expense report.  If your intention is to prevent charging beginning with a particular date, you may want to consider also using the Enforce Project / Task Dates project profile setting and supply an end date.