Client-server architecture is a software design in which one component, the server, stores data or provides a service, and another component, the client, requests and uses that service. The client usually handles the user interface and local actions, while the server manages shared resources, authentication, storage, or processing.
In cyber security, this split matters because each side has its own attack surface. An attacker may target the server to steal data, disrupt availability, or reach connected clients, or target the client to capture credentials, run malicious code, or pivot into the server. Defenders need to secure both ends with patching, access control, encrypted connections, logging, and version tracking. If only one side is updated, the environment can stay exposed even when the other component is fixed.