What are Registry Keys?

Keys to programs that have been registered by Windows. Installing a program or game adds keys (information) to Windows registry. In the registry there are main keys and sub keys which contain values written in binary codes about the program. The keys instructs the program such as a trial program that stops working after a certain time period. That is why when you uninstall a trial program and reinstall it, you still cannot use it because the information is still in the registry.