Is there a relationship between the price development of fund A and fund B and if so, how strong is this mutual relationship. We call this relationship between two funds the correlation and it can be positive or negative. A negative relationship means that if the price of fund A rises, the price of fund B falls. A positive relationship means that the price of fund A and fund B are moving in the same direction. That can be: rising or falling.
The strength of the relationship is a number between -1 and +1. If the correlation between two funds has the value 1, then that means that both develop exactly the same. With a value of -1 this is exactly the other way around. A correlation of 0 means that there is no (numerical) relationship whatsoever between the price development of both funds.