Means your flight isnt going to be leaving in the near future. Chances are the airline crew for your flight arent even in the same city, and wont be untill well after your flight was supposed to land. Usually announced after a "late inbound aircraft" delay and before "engineering requirements" cancellation.
Delta Flight 1182 has been further delayed due to "Crewing Requirements"
by flyingspikes April 30, 2009