Client
also: clients, client side, client-side
The program or device that asks another computer for information, like your web browser or a phone app. It then shows you what comes back.
The side of a client-server exchange that starts the conversation. Browsers, mobile apps and command-line tools act as clients when they send requests to a server and handle the responses. "Client-side" code runs on the user's own device.
A client is a customer at a counter. They ask for something, the person behind the counter fetches it, and the customer takes it away. The customer always starts the conversation.
Agents say "client-side" to mean code running on the user's own device. Anything there can be seen and changed by users, so it's no place for passwords, private keys or rules that must be enforced.
The email service's secret key is exposed on the client. Anyone who opens the browser's developer tools can copy it. I'll move that code to the server.
Keep the price calculation off the client. Do it on the server and only send the final total to the browser.
Thinking "client" means a paying customer. In software, it means the program or device making the request, usually a browser or an app.