On Device defines application functionality that operates entirely on the CPU of the device operating system it is installed on. This contrasts with applications that use remote servers (cloud infrastructure) to perform data processing.
Cloud infrastructure enables developers to leverage powerful computers to do heavy processing and massive data collection for building data lakes. These data lakes are often shared and sold to third parties.
On Device applications are self contained and do not offload processing to remote servers. It encourages highly optimized applications that have minimal impact on local CPU resources. This provides greater data privacy and security since data is not being sent from the device.