An aberration is something strange that rarely occurs. An example of an aberration is when the temperature in Minnesota hits 90 degrees in January — it's nice and warm, but it's really strange.
The noun aberration often refers to something that doesn't fit with current moral standards, or is something that shows a mental lack of control. Aberration comes from the Latin word that means "to wander, go astray." Today, you'd say it was an aberration to send little children to work in coal mines and factories and not to school, which was common in the nineteenth century. There's a very old poem called "The Chimney Sweep" about a boy who cleans chimneys and is only about five years old!