example: an
airplane crossing the
Atlantic passes the point (
somewhere beyond the center point of the
flight, hopefully) after which it would be
impossible to successfully return to the point of
origin; there is not enough
fuel to make it so turning around would result in the plane running out of fuel and plunging into the
ocean.
Having passed "the point of no return" does not neccessarily involve planes or crashes; the term can be used to express determination toward the completion or realization of some goal, project or end.