Periodically selling down whatever has grown into an oversized share of your portfolio and topping up what has shrunk, to return to your intended weights. Left alone, a winner compounds into a concentration risk you never chose. It forces the unnatural act of trimming your best holding, and on the PSE each adjustment costs commission plus the 0.6% tax on the sell, so most people do it once or twice a year rather than continuously. PSEye shows the current weight of every position.
See every term in the full PSE investing glossary.