A "criminal act" refers to an action or behavior that is against the law and can result in punishment by the legal system. It means doing something illegal that can lead to charges and potentially being convicted as a criminal. Full definition
As the gig economy grows, stories of consumers being harmed by criminal acts of providers can be expected to increase. (ere.net)
The first is what he called the «couple bad apples» theory: that most lawmakers are honest and not committing criminal acts in office. (buffalonews.com)
This is especially true of students who have committed criminal acts in or outside of school. (educationnext.org)