Idea
The word idea is an abstract thought or concept which people use to communicate their beliefs or plans. Generally, an idea is a plan one conceives for action. Less practically, an Idea, (capitalized), is a central meaning or purpose, it's a notion, an opinion.
Different definitions of idea
The New Oxford American Dictionary defines will in the following ways:
1. a thought or suggestion as to a possible course of action. For example, "They don't think it's a very good idea."
2. a concept or mental impression • our menu list will give you some idea of how interesting a low-fat diet can be.
3. an opinion or belief • nineteenth-century ideas about drinking.
4. (the idea) — the aim or purpose. For example: "I took a job with the idea of getting some money together."
5. [Philosophy] (in Platonic thought) an eternally existing pattern of which individual things in any class are imperfect copies. See: Ideal
6. (In Kantian thought): a concept of pure reason, not empirically based in experience.