hijacking on the high seas or in similar contexts; taking a ship or plane away from the control of those who are legally entitled to it
"air piracy"
the act of plagiarizing; taking someone's words or ideas as if they were your own
"The author faced legal consequences when it was revealed that his entire book consisted of nothing but piracy of existing literature."
Robbery at sea, a violation of international law; taking a ship away from the control of those who are legally entitled to it.
"The crew fought back against the pirates who had seized their merchant vessel in the middle of the Atlantic."
In plain English: Piracy is stealing things that belong to someone else, especially by attacking ships at sea.
"The government launched a new operation to combat music piracy on file-sharing websites."
Usage: In modern contexts, piracy often refers broadly to unauthorized copying or distribution of digital media rather than just robbery on the high seas. Be careful not to confuse this legal term with "piracy" in the sense of a pirate's personal loot, which is simply called plunder.
The word piracy comes from the Medieval Latin term piratia, which was derived from the Ancient Greek word for "robbery at sea." It entered English through this lineage to describe the act of stealing on the ocean.