The word "notion" refers to a general idea or understanding of something. It often implies a belief or opinion about a particular subject. Notions can be vague or well-defined, and they are usually formed as a result of personal thoughts or experiences. For instance, when someone says they have a notion about how things should work, they are expressing their perspective or belief.
The word "notion" comes from the Latin notio, meaning "a concept, idea, or understanding," which is derived from the verb notare, meaning "to note or to mark." The term has evolved over time through Old French before arriving in the English language.