Historically:
* A bailiwick was a territory under the authority of a bailiff, a medieval official responsible for administering justice and collecting taxes.
Modern Usage:
Today, "bailiwick" is used figuratively to describe someone's area of expertise, skill, or knowledge. It emphasizes the domain where a person feels most comfortable and capable.
Examples:
* "Music composition is her bailiwick; she's a genius at creating melodies."
* "Foreign policy is not my bailiwick; I'm more familiar with domestic issues."
Essentially, "bailiwick" implies a kind of ownership and mastery over a particular subject or activity.