Efficiency is the proportion of material removed under a defined test condition. In a cyclone separator, it describes how much dust is captured from the airflow rather than escaping out of the outlet. The number only has meaning when the test setup is fixed: particle size, airflow rate, dust load, duration, and measurement method all affect the result.
This matters in cybersecurity because many defenses are judged by the same idea: how effectively they remove, block, or detect unwanted material without slowing normal operations. A malware scanner, email filter, or web gateway may look strong in a lab, but its real value depends on the exact conditions used to measure it. Attackers also optimize efficiency, trying to deliver payloads or evade detection with the least cost and noise. In both cases, a headline percentage is useful only when the test conditions are clear and repeatable.