Correlation is the statistical linear correspondence of variation between two variables. It combines two related statistical concepts: variance and standard deviation.

Visa is a component of the S&P 500, so there could be a co-correlation between the variables here. There are only 20 observations, which may not be enough to make a good inference.

Correlation measures the linear relationship between two variables. By measuring and relating the variance of each variable, correlation gives an indication of the strength of the relationship.