Flightplan Departure Time?
 

What is the exact definition of a departure time marked in a flightplan? I haven't been able to find an unambiguous answer despite of my search. I wonder if it is the clearance request time or is it the actual take off time?

The UK Flight Planning Guide, which I think just replicates ICAO 'rules' and adds a bit of additional guidance, says that the time in item 13 for a FPL submitted before departure should be the estimated off-block time (EOBT).