Catastrophic Illness Insurance
  
"Cat" is a category of insurance. It's a way to protect against a huge illness wiping you out financially. The idea is that with this insurance, you just pay for small things out of pocket. Regular doctor's visits, your run-of-the-mill boo boos. But for something awful, like cancer, there's the catastrophic insurance.
Think of it like regular health insurance with a really high deductible. Because it only kicks in when the bills get stratospheric, the premiums are relatively small. On the other side, some of these policies also come with a cap...a total amount that the company is willing to pay out.