What is the definition of juviniles?

Answer 1

The general answer is that a juvenile is any individual under the age of adulthood under the laws of the state or nation they are in. In the United States and in most nations today, people stop being a juvenile on their 18th birthday. In Japan the age is 20.

If you are talking about criminal justice the law is more complex and in most nations, including the US, children who commit particularly heinous acts can be charged as if they are an adult. In the US each state sets its own regulations regarding how that will occur and when. The federal court system has a set of rules for use in federal prosecutions.

Answer 2

a juvinile is what you call a criminal under the age of 18 a "kid" criminal