An AI application is a product that uses an AI model to help people do something. The model is one part of the product; the app may also give it instructions, useful information, and tools.
For example, a travel helper might receive a person's question, look up saved trip details, and suggest an itinerary. The surrounding app decides what information the AI can see and what actions it is allowed to take.
AI can make mistakes, so important answers should be checked. A useful app makes its limits clear and does not assume that a confident-sounding response is always correct.