A Kaizen is a Japanese term that refers to a long-term approach that systematically seeks to achieve small incremental changes in processes in order to improve efficiency and quality.

In other words, Kaizen is the Japanese equivalent of continuous process improvement. Kaizen can be applied to any kind of work, but it is perhaps best known for its use in the lean approach to process improvement.  Masaaki Imai made the term well-known in his book "Kaizen: The Key to Japan’s Competitive Success".