Need the detail or description of permission.C2D_MESSAGE

Question

In my app, I use the GCM push notification. All sample app for push notification has this two permission. I need to know the reason for this permission. I couldn't find any documentation of permission.C2D_MESSAGE permission.

<permission android:name="YOUR_PACKAGE_NAME.permission.C2D_MESSAGE"
        android:protectionLevel="signature" />
<uses-permission android:name="YOUR_PACKAGE_NAME.permission.C2D_MESSAGE" />