Not to be pedantic but I've only heard it referred as D&O insurance. The directors come first and its relatively expensive: google quotes $5k a year per million of coverage.
Also not all things are covered and it can be litigated (in my limited experience) to force the insurer to pay. Plus you can still do something that gets you personally in trouble even with coverage.
Obviously, a sweet gig and incredibly hard to get. But everything has some hair around it.
