While "plan" and "policy" are related terms, they are not exact synonyms and are used differently in various contexts.
In summary, a plan is usually a specific, actionable set of steps designed to accomplish a particular objective, whereas a policy is a overarching principle or rule intended to guide consistent decision-making across situations.
Although they can overlap in certain contexts, plan and policy are not perfect synonyms. A plan might be created to implement or support a policy, but they serve different purposes within planning and organizational frameworks.