Definition: Google Cloud Messaging
A service that allows messages to be forwarded by Google to Android devices. An app developer sends a message up to 4KB in length to Google servers that are in turn sent to users that have its app installed. It can be an instant message or a notification to the user to download an update. In the summer of 2012, Google Cloud Messaging (GCM) superseded the Android Cloud to Device Messaging (C2DM) service.