The Oxford Dictionary defines a crime as
an action or omission which constitutes an offence and is punishable by law. A crime is a fact, a matter of law and it is not an opinion. As society changes, some actions which used to be criminal are no longer so. Likewise some actions which were legal can become prohibited.
An example of this is the introduction of by-laws which allow local authorities to prohibit drinking in designated public places. Laws are made by the politicians we elect democratically - we may not agree with the law but there are democratic opportunities to change it.
In a democratic society someone charged with a crime has the opportunity to defend him/herself. He or she will be deemed innocent until proven guilty by a criminal court. Punishments traditionally reflect the seriousness of the crime, the most serious are those which involve violence and/or loss of life.
The causes of crime are complex. Poverty, parental neglect, low self-esteem, alcohol and drug abuse can be connected to why people break the law. Some are at greater risk of becoming offenders because of the circumstances into which they are born.