SafetyNet Evaluatuion verifies the device safety with SafetyNet compatibility tests and evaluate the result.
The SafetyNet API is a part of Google Play Services Framework. Some apps (e.g bank apps) use this API to check whether the device has been rooted or tampered. If your device is rooted or you have custom ROM installed then your device won't pass this test. There have been some methods to pass this check with rooted devices. You can get more information about how to hide root in relevant threads on XDA Forums.