A crime is when a person does something that is against the laws of a country. A person who does this is called a criminal.
The basic idea of what things are called crimes is that they are thought to be things that might cause a problem for another person. Things like killing another person, injuring another person, or stealing from another person are crimes in most countries.
But different countries have many different ideas of what things are crimes. Some things that are crimes in one country are not crimes in other countries. Many countries get their ideas of what things are crimes from religions.
In many countries, if people say they made or wrote a book, movie, song, or Web page that they didn't really write or make, it is a crime against the laws of copyright. In many countries, helping to grow, make, move, or sell illegal drugs is a crime.
In most countries, police try to stop crimes and to find criminals. When the police find someone who they think might be a criminal, they usually hold the person in a jail. Then, usually, a court or a judge decides if the person really did a crime. If the court or judge decides that the person really did it, then he or she might have to pay a fine or go to prison. Sometimes the judge might decide that the criminal should be executed (killed). This is called Capital punishment (or the Death Penalty). There are countries in the world who execute criminals, and others who do not.
When some criminals make money from crime, they try to stop the police finding out where the money came from by money laundering. (Credit: Wikipedia)