A correlation is a relationship between two things, or variables.
For example, it is generally true that the more junk food you eat, the fatter you get. This is a positive correlation – there is a strong relationship between the two things.
A negative correlation means that there is a strong relationship between two variables, but in the opposite direction. For example, the older a second-hand car is, the lower the price.
Zero correlation happens when >there is little or no relationship between two things- when they don’t affect each other. For example, the number of times you go to the movies in a year is probably not related to the number of brothers and sisters you have… or is it?