This task concern constraints on one table only.

Two indexes i1 and i2 are called constraint correlated if some of their parts are contained in the same constraint.

For example:
Consider table lineitem from dbt3 benchmark.

Index i1: on lineitem(l_shipdate)
Index i2: on lineitem(l_receiptdate)

And let's add constraint c on lineitem: l_shipdate < l_receiptdate
(can be easily checked that it is true for the lineitem table)

As i1 l_shipdate and i2 l_receiptdate both participate in c, indexes i1 and i2 are constraint correlated.