On-device AI refers to running AI models directly on end-user devices — smartphones, tablets, wearables — rather than in the cloud. This eliminates network latency, works offline, and keeps sensitive data on the device, improving privacy. Apple's on-device models, Google's Gemini Nano, and Samsung's Galaxy AI demonstrate this trend. Quantization and model compression make on-device inference practical, though models are necessarily smaller than their cloud counterparts.