A plan is a set of actions that have been thought of as a way to do or achieve something. It is something that a person intends to do. This is Merriam-Webster definition.
In everything that we do, there is always a plan whether well-thought off or not. Ideally, the plan is well-thought off.
Well-thought off plans consist of the both expected and unexpected plans. Expected plans are the usual plans, those that a person thinks will happen if he has a certain set of actions. However, in the real world, not all expected plans are and can be implemented smoothly. There will always be glitches and hitches. Thus, contingency or unexpected plans should also be formulated together with the expected plans. A contingency plan is a course of action to be followed if a preferred or expected plan fails or there are glitches and hitches.