A slap on the wrist is a punishment that is very mild. Example: "He should be in jail for what he did, but he got off with just a slap on the wrist."

When the punishment turns out to be less than was expected, it is considered a slap on the wrist. Example: "You got off easy this time, but stealing is a serious crime and next time it won't just be a slap on the wrist."

A slap on the wrist is a light, almost gentle punishment for doing something wrong. Example: "The police have gotten very serious about prosecuting drunk drivers. Nowadays you don't just get a slap on the wrist; they will throw you in jail."