Noun

1. The point in an aircraft's flight when there is insufficient fuel to reverse direction and return to the place of origin.
2. The point in any journey, process, or sequence of events when it is no longer possible to reverse course or stop the process.
   • 2005, Steve Connor, "Global warming 'past the point of no return'," The Independent, 16 Sep.:

   A record loss of sea ice in the Arctic this summer has convinced scientists that the northern hemisphere may have crossed a critical threshold beyond which the climate may never recover.