Douglas Burgess Jr. makes the interesting argument that pirates are a type of terrorist and should be treated as such.
The solution to piracy lies in the very nature of piracy itself. The Roman lawmaker Cicero defined piracy as a crime against civilization itself, which English jurist Edward Coke famously rephrased as "hostis humani generis" — enemies of the human race. As such, they were enemies not of one state but of all states, and correspondingly all states shared in the burden of capturing them. . . .
Pirates are not ordinary criminals. They are not enemy combatants. They are a hybrid, recognized as such for thousands of years, and can be seized at will by anyone, at any time, anywhere they are found.
. . . Are pirates a species of terrorist? In short, yes. The same definition of pirates as hostis humani generis could also be applied to international organized terrorism. Both crimes involve bands of brigands that divorce themselves from their nation-states and form extraterritorial enclaves; both aim at civilians; both involve acts of homicide and destruction, as the United Nations Convention on the High Seas stipulates, "for private ends."
It is an interesting argument, but it may have a faulty premise. As Kevin Jon Heller notes, while pirates may be enemies of all states, that does not make them the same as terrorists.
The defining feature of terrorism is precisely that it is committed not for private ends, but to intimidate a civilian population or to influence government policy. Indeed, over the long and troubled history of efforts to create a general definition of terrorism, that is perhaps the only aspect of the definition that has never seriously been in doubt. . . .
Pirates have no politics. They are, therefore, not terrorists.