What does Correlation mean?

Correlation is a way of telling if two money things go up and down on the market at the same time. If they go up and down at exact same time, they have a positive correlation, +1. If one goes up when the other goes down, they have negative correlation, -1. Owning money things that go exactly in the opposite direction to each other is a good way to reduce risk, because it means that when one goes up, one goes down, and you have balance.