A Murphy's-law variation where all the possible things that can go wrong coincidently happen at the same time or on the same project.
The phrase came from a movie based on the true story of a boat of fishermen being pummelled by a huge storm that was a result of coincidentally horrid weather conditions. The movie seems to have popularized the term; OTOH I have a hard time believing that it (or whatever book it may have been based on) coined the term.
Example: Being hired by Enron in 1999 and deciding to put all your savings into dot-com stocks and having the name "Gray Davis", the same as the California governer.
Often times caused by a CascadeFailure?--in many cases, the claim that n simultaneous failures occurring is a mere unfortunate coincidence is wrong. See also DefenseInDepth.
If the failures are related, then it is not a PerfectStorm, but probably just bad management using PerfectStorm as an excuse.
And a common excuse it is; I've heard many managers blame poor financial results, late/cancelled projects, or other things on a "perfect storm". Of course, PerfectStorms do occur, you cannot plan for every contingency. But many managers create the weather conditions necessary for PerfectStorms through their errors.
If the failures are related, then it is not a PerfectStorm,
I agree, my understanding is that, in a perfect storm, all possible multiple unrelated failures occur at the same time. For example, a perfect storm would apply to the situation where all the following occur simultaneously: your washer's overflowing, toaster's catching fire, freezer's breaking down, car's not starting, major earthquake is hitting your city and your wife is giving birth in the back yard. (maybe you're having some sort of seizure in the middle of it to boot).