What is the name of the pirate flag with skull and crossbones?

The Jolly Roger, though there was never one standard design - individual captains flew their own, and the skull and crossbones was only one motif among hourglasses, bleeding hearts, whole skeletons and raised swords. Blackbeard's reportedly showed a skeleton spearing a heart.

It was a piece of practical psychology rather than bravado. The flag meant surrender now and you will not be harmed; a plain red flag, which the French called the jolie rouge and which is one proposed origin of the name, meant no quarter would be given. A crew that gave up without a fight kept their lives and the pirates kept the cargo undamaged and took no casualties. Terror was cheaper than combat, and the reputation did most of the work.

The whole era was brief. What is called the golden age of piracy in the Atlantic and Caribbean lasted roughly from the 1650s to the 1720s and was largely a by-product of European wars - privateers licensed to attack enemy shipping, left unemployed at each peace. Ships also ran surprisingly democratically, with elected captains, written articles agreed by the crew, and compensation set out for specific injuries, at a time when naval sailors had none of that.