A question from Yahoo! Answers:

What was privateer?

Basically, a pirate turned mercenary. The word was used to designate both the vessel and its captain. Between 1500 and 1800, all significant naval powers employed privateers. Privateers attacked military and civilian targets belonging to their employer’s enemy and pillaged them for profit (or received monetary rewards from their employers for destroying specific targets). Normally, privateers were not under any naval command and were by and large free to do what they pleased.

Most European countries abolished privateering in early 19th century. The Paris Declaration of 1856, signed by most European governments, created an international law forbidding privateering.

The last episode of large-scale privateering occurred during the Franco-Prussian War of 1870, when Prussia created a “volunteer navy” of private ships eligible for prize money. However, unlike classic privateering, the “volunteer navy” sailed under a centralized naval command, and its members were required to adhere to regular naval discipline.