Severance Package
  
When you're a player, a valuable manager in a company, and you get fired (or "severed" from the company), you have a number of dials that get turned to make you go away nicely and quietly, while saying good things about the company to the press. So, as part of your firing process, you'll get something like 5 or 10 or 20 weeks' salary as a parting gift "bonus." You'll get to vest forward into 3-6 months' worth of stock options that you were previously granted. You'll get benefits to continue another quarter or two until you have to buy your own insurance. Your 401(k) matching contributions might continue another year.
It's a load, and yes, it costs a fortune for a company to fire a CEO, CFO, or other top level officer. And why would it cost so much? Like...if they're being fired, then they ran the company poorly. So why all the dough to just make someone go away?
Lawyers. Crazy juries. Weird verdicts from juries who scare company lawyers.