Quote from ZAL:
A hedged or commercial market is one that contains a high percentage of participants who are hedgers or actual producers & users of a commodity or financial instrument.
A farmer or a grain elevator operator is an example of a producer. A baker or pasta maker is an example of a user. Producers and users must hedge their exposure of a cash commodity (like Wheat) in the futures market.
Physical commodities and financial intruments (like US Treasury Bonds) have a high component of hedgers and users. Unlike the S&P index which has a high component of pure speculators.
A market that contains a 50% hedging component and a 50% speculative component is a better market for a trader to participate in.
Not sure about the correlation, but there is lots of hedging in the ES