It means you supply the key for the AI model provider, and the agent uses it. You create a key with the model provider you choose, add it to Emolysis once, and it is kept in your machine's credential store. Requests go to that provider under your key, and the provider bills you directly at its own rates.
Emolysis does not charge for model usage on the Free plan, and it adds nothing to your provider's bill. You can change or remove the key at any time.
The trade-off is that you manage the key, your spending limits and the provider's terms yourself. Pro, Max and Team include model usage, so you do not need a key there, and every paid plan still accepts your own key. See model keys and credits and the post bring your own key.