Blue-collar crime is a term given to criminal acts more likely to be committed by citizens of lower social class in society, such as those which inflict direct harm on the person or property of others. This is in contrast to white-collar crime, which is generally committed by citizens of higher social class, who are more likely to be presented with the opportunity to commit such crimes.
"Blue-collar crime" is an informal classification and holds no particular legal weight. For the most part, blue-collar crime entails whatever crimes are most immediately possible for a person to commit, those that are most often spurred by passion rather than those that require careful deliberation. Crimes against the person, crimes against property, and many forms of victimless crime such as prostitution, gambling and drug abuse all tend to be classified as blue-collar crime. Blue-collar crimes are, for the most part, those that cause an immediate and highly visible injury to society, so they're usually punished much more rapidly and severely than white-collar crime. Also, citizens of lower social class cannot generally afford high-quality legal assistance, which means they tend to suffer far more severe punishment than white-collar criminals.
Citizens of higher social class are certainly capable of committing "blue-collar" crimes, and do, all the time. However, the vast majority of these crimes are committed by citizens of lower social class, who in turn have limited opportunities to commit white-collar crimes such as financial fraud and money laundering, which is how these classifications originated.