The term pirate referred to the variety of rogues that were scattered across The Galaxy who would attack, rob or commandeer ships in their territory.
Whilst their actions were inherently illegal, the morals of various pirates varied considerably. Some were cutthroat brigands who were petty murderers or thieves, but others, such as Nym, had a set of morals that prohibited killing the innocent, and generally restricted their actions to the rich.
Indeed, on a few occasions, pirates have pulled through to help the galaxy as a whole.
Mostly though, they are the scourge of The Galaxy.