A four-step model used in management. This is a pillar for a management system.

IATF definition:

Plan: establish the objectives of the system and its processes, and the resources needed to deliver
results in accordance with customers’ requirements and the organization’s policies, and identify
and address risks and opportunities;
Do: implement what was planned;
Check: monitor and (where applicable) measure processes and the resulting products and services
against policies, objectives, requirements and planned activities, and report the results;
Act: take actions to improve performance, as necessary.

IATF 16949:2016