Step 1: Understanding the Concept:
A 'victimless crime' is a term used for an illegal act that typically either directly involves only the perpetrator or occurs between consenting adults. In such crimes, there is no direct, complaining 'victim' in the traditional sense. The act is prosecuted because society, as a whole, considers it harmful.
Step 2: Detailed Explanation:
Let's analyze the options:
1. Drug Abuse: The act of consuming illegal drugs is a classic example of a victimless crime. The primary person being harmed is the user themselves, who is also the perpetrator. While it has indirect societal costs, there isn't a direct victim who files a complaint.
2. Robbery: This is a crime with a clear and direct victim, from whom property is taken by force or threat of force. It is a quintessential crime against a person/property.
3. Cyber crime: Most cybercrimes, such as hacking, fraud, and identity theft, have clear and direct victims who suffer financial or personal harm.
4. Communal rioting: This is a crime against public order and involves violence against individuals and communities. It has numerous direct victims.
Step 3: Final Answer:
Among the given options, drug abuse is the one that fits the definition of a victimless crime, as the act itself does not have an immediate and direct external victim.