Correlation matrix
A table of pairwise relationships between the assets in a portfolio: it shows which positions duplicate each other and which live their own lives.
How to read the number
It is read in groups rather than cell by cell: a cluster of tightly related names is one large bet, however many lines it occupies in the list.
When the metric lies
The relationships are not stable. In a crisis correlations between risky assets converge towards one exactly when their differences were being relied upon, so a matrix taken from a calm year promises diversification that will not be there on the day it is needed.
Also known as: matrix of pairwise correlations