The phrase "good behavior" refers to a person's conduct or actions that are considered acceptable, polite and proper. It is often used in legal contexts when referring to an individual who has been convicted of a crime and is being sentenced by a judge. In this case, good behavior means the offender follows all rules and laws while serving their sentence without any further issues or incidents. The term can also be used more broadly to describe someone's general conduct in everyday life - for example, behaving well may mean treating others with respect, being polite, following social norms, and abiding by the law.