Do you have an idea of what you want and have thought carefully and in detail about how to get it? Then you have a plan, a series of actions required to achieve a particular goal.
A plan can exist only in your head, or it can be a physical object, such as an architectural plan of a building, showing how you propose to build it. As a verb, plan means the act of thinking about how to achieve your aims. You might plan to apply to colleges soon. When you plan something, you're laying the seeds for a future result, so it's not surprising that plan comes from the early English word plante, meaning "seedling."