Banditry is not a person. It is the work bandits do: robbing people, often in a group, and often by attacking travellers on the road. The person is a bandit; banditry is the activity, the kind of crime. You meet it in history, in news about unsafe hills or borders, and in stories — “the mountain roads were full of banditry.” It sounds a little bookish. In ordinary talk people more often say robbery, raids, or “they were robbed by bandits.” Though actually, it is narrower than all stealing: a pickpocket in a night market is not banditry. The word still carries an old picture of the open road, even when the report is modern.