A sub-millisecond power ramp is a very fast change in electrical load that happens in less than one thousandth of a second. In practice, it means a device or workload can move from low power to high power almost instantly, creating a sharp transient instead of a gradual rise.
This matters in cyber security because modern attacks can exploit workload timing as a physical control signal. In shared GPU or cloud environments, tightly synchronized compute bursts may produce rapid load swings that stress power supplies, UPS systems, or nearby electrical infrastructure. Defenders care about ramp rate, not just average consumption, because sudden transients can trigger power-quality events or expose weak buffering and telemetry. Mitigations include workload smoothing, per-rack power monitoring, local power conditioning, and limits on how quickly large jobs can start or stop.