Intermarket analysis is the study of how markets interact with each other. Intermarket analysis is the study of how different markets like stocks, bonds, commodities interact and correlate with each other.
For example, when interest rates increase, bond price will decrease. The relationship between bond price and interest rates is one of the most obvious negative correlations.
Another example is how the U.S. Dollar direction drives some commodities like Gold. When the U.S. Dollar is rising, it often drives Gold down.
International stock markets are similarly driven by the direction of the U.S. Dollar for U.S. investors. When the U.S. Dollar is rising it makes International investments less profitable because income and gains from those investments are reduced by the exchange rate when converted to U.S. Dollars