Refers to armed outlaws or rebels, often in a historical or literary context. Not an everyday word for a thief.
その地域は匪賊の襲撃に悩まされていた。
The area was plagued by bandit raids.
The kanji 匪 means 'bandit' or 'rebel', and 賊 means 'thief' or 'rebel'. The compound is a Sino-Japanese word (kango) combining these two similar meanings.