The taxman brings a prediction!
"Yikes, the Omnibus Bank of BotB is in the red! Everyone will be paying 20% next May!"
DOS stands for Disk Operation System and usually refers to a family of operation systems dominating on the IBM PC compatible computer market in the period 1981-1995. The most well-known example of this family is Microsoft's MS-DOS.
If you want to run DOS programs on your (presumably modern) OS, check out DOSBox.