Real Dictionary

idea
An idea is a plan, suggestion, or possible course of action.
An idea is an opinion or belief about what something is like or should be like.
If you have an idea that something is the case, you think that it may be the case, although you are not certain.
countable noun: If you have the idea of doing something, you intend to do it.
singular noun: If someone gives you an idea of something, they give you information about it without being very exact or giving a lot of detail.
singular noun: If you have an idea of something, you know about it to some extent.
singular noun: The idea of an action or activity is its aim or purpose.

idea in American English
something one thinks, knows, or imagines; a thought; mental conception or image; notion
noun: any conception existing in the mind as a result of mental understanding, awareness, or activity