Index options are considered to be the "smart" money, while individual stock (equity) options, are the "dumb" money. Unusually high index put or call volume normally says that the large institutional investors, who make up about 50% of the market volume, are placing their bets on the movement of the underlying instrument for the next several trading days. Moreover, if they then trade the underlying instrument in the direction of their option, it can become self-fulfilling. The following link discusses this well-known effect...
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