The trained core of an AI: a big bundle of numbers that turns an input into an answer.
In AI, a model is what you get after training. Think of it as a large file: a fixed recipe for how to calculate, filled with numbers (parameters) that training has tuned. Give it a question or a photo, and it runs those numbers to produce an answer.
The chat app you use is the window; the model is what actually writes the reply inside it. An app can swap one model for another, and one model can power many apps. Models come in all sizes, from huge ones that only run on servers to small ones that fit on a phone.
Think of it like this
Think of a music app and a song file. The app gives you buttons and a screen; the actual sound lives in the file. With AI, the app is the window and the model is the part that makes the answer.
For example
When an app says it has "switched to a new model", the window stayed the same but the core inside changed.