Plain English Meaning
The set level of skill and knowledge a pilot has to reach and prove before they are considered ready to fly a particular airplane on their own.
Full Definition
The defined level of knowledge and skill a pilot must demonstrate to be considered competent in a specific airplane, operation, or task. In transition training, proficiency standards are the measurable performance criteria — such as airspeed tolerances, altitude control, configuration management, and procedural accuracy — that the pilot must meet before being signed off to operate the new airplane safely.
Context Anchor
Seen in transition training when describing the skill level a pilot must show before being considered ready to operate a different airplane or move to the next training step.