A backend dependency is a service or system that a customer-facing application relies on but that users may not see directly. Examples include identity and authentication services, order-processing systems, payment integrations, and databases. If a dependency is unavailable or impaired, an app may fail even when its own interface is working.
In cyber security, backend dependencies matter because an attack or outage affecting one can disrupt multiple services, expose connected systems, or complicate recovery. During an incident, teams may restore customer-facing features in stages while testing dependencies, monitoring activity, and confirming that systems are safe to reconnect. Mapping dependencies and planning for failure helps organizations limit disruption and restore services more securely.