PDCA standard for Plan-Do-Check-Act. It is not unique to ISO 27000, or to information security, but rather a simple approach to developing and improving an organizxation's management system. It is commonly adopted for implementation of ISO27001

The following diagram illustrates the model:

The cycle was designed to be used as a dynamic model, with the end of one turn of the cycle flowing directly into the start of the next, the idea being one of continual improvement.

It was originally devised by Walter Shewhart in 1920's and 30's, but later further developed by W Edwards Deming. In fact it is sometimes known as the Deming Cycle, and also the PDSA (Plan-Do-Study-Act) Cycle.