1. Something conceived in the mind (Source: Merriam-Webster's Collegiate Dictionary. https://www.merriam-webster.com/dictionary/concept)
2. Concepts are the constituents of thoughts. (https://plato.stanford.edu/entries/concepts)
3. In metaphysics, and especially ontology, a concept is a fundamental category of existence. In contemporary philosophy, there are at least three prevailing ways to understand what a concept is (https://en.wikipedia.org/wiki/Concept):
- Concepts as mental representations, where concepts are entities that exist in the mind (mental objects)
- Concepts as abilities, where concepts are abilities peculiar to cognitive agents (mental states)
- Concepts as Fregean senses (see sense and reference), where concepts are abstract objects, as opposed to mental objects and mental states
- “concepts” are sometimes interpreted as “properties” or “categories"
- It has been suggested that the term 'concept' not be used in the context of applied ontology due the several definitions and the attendant expectations engendered by those definitions. Instead use the term 'notion'.