Kaikaku (改革, or かいかく in hiragana) = radical change, reform
Kaikaku means a radical change, during a limited time, of a production system. Kaizen, on the other hand, is continuous minor changes of a certain area of a production system, often with the primary goal of solving team related problems. A cross between Kaikaku and Kaizen is Kaizen Blitz (or Kaizen Events), which implies a radical improvement in a limited area, such as a production cell, during an intense week.
Kaikaku is about introducing new knowledge, new strategies, new approaches, new production techniques or new equipment. Kaikaku can be initiated by external factors or when management see that ongoing Kaizen work no longer provides adequate results in relation to the effort.