Date Certain

Contracts for all kinds of business transactions are predicated on calendar dates for obligated events to occur. Drop dead dates and payment due dates are "date certain" events. If you've ever received a deadline to hand in a report, an eviction notice, an express courier package delivery or a lottery ticket, you also have date certain schedules for when events or announcements have to occur and failure to comply will often find you in default or worse.

In the financial world, stock options contracts, which expire the third Friday of every month at market close, are fine, loving, excellent Date Certain examples.