Until loops are just the opposite of whiles. If the control statement evaluates to false code within the loop is executed once and repeated until the control statement tests to true.
Heres a quick example:
   print "Mission-critical electronics working in the year $year\n";
   #now it works;
print "Not working anymore\n";
As you can see the mission-critical electronics work until the year 2000.
I suggest if you've just survived that harrowing ordeal you learn all about do while loops