Reentry is the phase when a spacecraft passes back through a planet’s atmosphere. It is one of the most demanding parts of flight: high speed, compression, and friction produce extreme heat and mechanical stress, so engineers model it carefully to verify thermal protection, trajectory control, and structural margins.
In cyber security, reentry is often used as a metaphor for a system returning to service after isolation, reboot, or incident response. That matters because a host is not automatically safe just because it is back online. Attackers may use persistence to reenter a network after cleanup, while defenders use reentry checks such as integrity verification, patch validation, reauthentication, and heightened monitoring. The practical lesson is simple: reentry should be treated as a controlled, tested phase, not a routine restart.