What's an Idea?

An idea is a concept or abstraction formed and existing in the mind. Human capability to contemplate ideas is associated with the ability of reasoning, self-reflection, and the ability to acquire and apply intellect. Further, ideas give rise to actual concepts, or mind generalisations, which are the basis for any kind of knowledge whether science or philosophy.

In a popular sense, an idea arises in a reflex, spontaneous manner, even without thinking or serious reflection*
*Wikipedia