When you sign into your Gmail account, Google then tracks your search history. Within your search history there is a "Trends" link that displays details of your searches, images you've looked at and sites you've visited. This helps Google match targeted advertisements based on your preferences. If you would rather keep your search history hidden, you have the option of deleting it through the "My Account" feature.
Log into your Gmail account by typing in your username and password.
Click "My Account." You will see "Search History" beneath "Services."
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Click "Search History," "Clear Entire Search History." You can also click "Remove Items" and place a check next to the items listed that you want to delete and, then click "Remove."