filing date

The filing date of a patent application is the date the patent application was filed in one or more patent offices.In the United States, if a patent application is mailed to the United States Patent and Trademark Office (USPTO) by Express Mail, Post Office to Addressee, then the date the application was deposited in the post office is the filing date.
See more at Wikipedia.org...

the date of receipt in the Office of an application which includes (1) a specification containing a description and, if the application is a nonprovisional application, at least one claim, and (2) any required drawings 

-- see MPEP 506 for more

Context: Patent