The expression "Force majeure" has been a popular one in FIDE circles recently. It translates from French as "Superior Force" and is used as a legal clause that frees one or both parties in a contract from liability if an unforeseen and external event prevents the terms of the contract from being fulfilled.
FIDE President Kirsan Ilyumzhinov used it quite a lot in a press conference at the Dresden Olympiad to explain why his promised financial guarantees for the Topalov v Anand World Championship weren't really guarantees at all. However he failed to identify the external event that prevented his fulfilling his initial promises, leading some to assume the "Force Majeure" actually translated to "I've changed my mind".
However it looks like FIDE have got the usage right this time, in deciding to postpone the first game of the upcoming World Championship Match by one day. In this case the "Force Maejure" is the volcanic eruption in Iceland prevented air travel in Europe for the past week. The lack of air travel resulted in the late arrival of World Champion Viswanathan Anand in Sofia, who spent 40 hours on the road to get there.
Nonetheless at least one GM has observed that the delay may not be so much about Anand's travel difficulty, but the fact that FIDE officials are also having difficulty getting to the venue in time. Have a look at the Chessbase report and make up your own mind.