Yarg, matey! A cartoon pirate wears an eye patch, three-cornered hat, billowy shirt, and tall black boots. In real life, a pirate just boards ships and robs them of cargo, valuables, and money, often while wearing regular boring clothes.
Pirates have been around since humans have been shipping valuable goods by boat across oceans. You can also use pirate as a verb to describe what these robbers do. Today, in addition to traditional pirates, there are pirates who use digital creative material, like books, movies, games, and music, without paying for it. If you pirate a movie, you make a copy and sell it illegally. The Greek root of pirate is peirates, "one who attacks."