An exported activity in Android is an application component that is made accessible to other apps on the device. By default, activities are not exported unless specified in the app's manifest file or if they have intent filters. Exporting an activity allows external applications to start it, which can be useful for legitimate inter-app communication. However, if sensitive activities are exported unintentionally or without proper security measures, it can expose the app to security risks such as unauthorized access or data leakage. Developers must carefully manage which activities are exported and apply appropriate permissions to protect sensitive functionality.