Plain English Meaning
Training you come back to do again on a regular schedule after you've already earned your certificate, so your skills and knowledge stay sharp.
Full Definition
Periodic training that a pilot completes after initial certification to maintain proficiency, refresh knowledge, and stay current with regulations, procedures, and aircraft systems. It is required at set intervals for many types of flying (such as flight reviews every 24 calendar months for most pilots, and more frequent training for commercial and airline operations).
Context Anchor
Seen in discussions of pilot proficiency, return-to-flying plans, flight school programs, and professional requirements.