From Fallen London Wiki
Placeholder Quality Denoting the Current Week, That is to Say A Measurement of Time Which may Consist of Roughly Seven Days, When Measured Against the Total Number of Weeks Eclipsed Since the Start of Said Year, Which Is Used in Random Places For Text
(which, to be fair, is a wiki abstraction because the *actual* datamined hidden quality that governs these things can't legally be shown on the wiki)