Outbound transmission is data sent from a device or application to a destination outside that device or application, such as a remote server. It can be legitimate, as when software syncs files, or harmful, as when an attacker sends stolen data out of a system.
In cyber security, monitoring and restricting outbound traffic can help detect or prevent data exfiltration. For example, if untrusted content in a preview component can access local files, an attacker may try to transmit exposed credentials to an external server. Defenses include isolating renderers, limiting their network access, and watching for unusual destinations or unexpected data transfers.