Until now, your Google Web History (all Google searches and sites visited) has been cordoned off from Google's other products. This protection was especially important because search data can reveal particularly sensitive information about you, including facts about your location, interests, age, sexual orientation, religion, health concerns, and much more.
Therefore, if you want to keep Google from combining your Web History with the data they have gathered about you in all their other products, such as YouTube or Google Plus - you may want to remove all items from your Web History and stop your Web History from being recorded in the future.
Here's how you can do that:
1.) Sign into your Google account.
2.) Go to www.google.com/history
3.) Click "remove all Web History."
Note: Removing your Web History also pauses it. Web History will remain off until you enable it again. If you have several Google accounts, you will need to do this for each of them.