Date certain is a legal term for the date on or by which the actions of a

contract A contract is an agreement that specifies certain legally enforceable rights and obligations pertaining to two or more parties. A contract typically involves consent to transfer of goods, services, money, or promise to transfer any of thos ...

can be reasonably completed. Ambiguity may nonetheless result, for example when a contract requires that action be taken "by" a specified date that may mean either "by a certain date" or "on or before a certain date".

References

Legal terminology {{law-term-stub