There are three types of correlation.
1) Positive correlation: Two variables are said to be positively correlated when one variable increase then other variable will also increase or one is decrease then other will also decrease.
2) Negative correlation between two variables means when x is increasing but y is decreasing or vice versa.
3) No correlation: When the is scattred and we won't be able to find any distinct relationship then there will be no relation.
Notice in the first and third graph it has positive slope which means if x is increasing then y is also increasing. So, first and third graph is positively correlated.
Whereas in the second graph if x is increasing then y is decreasing. So, second graph is negatively correlated.
But in the last graph there is no such relationship as the data scattered randomly everywhere in the graph. So, it's shows no correlation.