Insurance Defense
  
You spend three hours navigating your insurance company's phone tree, just to get reimbursed for the $100 you were accidentally billed for your last doctor's visit. Eventually you get frustrated, throw down the phone, and murder the person standing next to you. After a lengthy trial, you are set free on a plea of temporary insanity...because everyone on the jury understood how dealing with an insurance company might drive a person to random slaughter. Insurance defense.
In reality, the term is much more boring. It just refers to a type of lawyer who specializes in cases involving insurance companies. Specifically, they defend insurance firms against lawsuits filed against them. Like...a class action suit filed by the families of all the people murdered by people driven crazy by insurance companies.