IT is whispered about at the margins of meetings, and discussed in Washington parties where rumour is passed around with the wine and canapes.
It even appears, fleetingly, to be fact.
"The day nobody died from violence in Iraq" is a date that has been much anticipated in the White House - where US President George W. Bush is desperate to hail the success of his surge of 30,000 troops this year.
But no one can quite say when this event occurred.
"It was some time this week, wasn't it?" says a senior military source. "Or maybe last week."
Another diplomatic official confidently asserted that there were "at least two such days this month". When, exactly? "Not sure," he replied.
Such vagueness may be concealing a truly significant transformation on the ground in Iraq.
There have certainly been several days in the past month when no US or British soldiers were killed.
During a five-day stretch between October 19 and 23, there were no deaths among coalition forces. Although three US servicemen died from "non-hostile causes", this was the longest period without combat deaths for almost four years. And, between October 27 and 29, there were more days without coalition deaths.
Such statistics do not take account of deaths among the Iraqi security forces or civilians. But Iraqis, too, have had days when no one in their ranks has died. On October 13, for instance, neither the coalition nor the Iraqi military suffered any deaths. But one Iraqi policeman was killed, along with four reported civilian deaths in Baghdad.
Two days later, there were no deaths among the coalition but six among the Iraqi security forces.
October 19 was a death-free day for both coalition and Iraqi security forces, but 12 civilians were killed.
The civilian death toll was lower on October 23 - when four were killed - but they were joined in the mortuaries by two Iraqi policemen.
On October 30, the Iraq Interior Ministry reported that there were no civilian deaths in Baghdad but three US troops and four Iraqi policemen were killed.
It is beyond dispute, though, that the tide of violence in Iraq has been stemmed. (Maybe Dahr Jamail will dispute it)