Logos (UK: , US: ; Ancient Greek: λόγος, romanized: lógos, lit. 'word, discourse, or reason') is a term used in Western philosophy, psychology and rhetoric and refers to the appeal to reason that relies on logic or reason, inductive and deductive reasoning. Aristotle first systemised the usage of the word, making it one of the three principles of rhetoric. This specific use identifies the word closely to the structure and content of text itself. This specific usage has then been developed through the history of western philosophy and rhetoric.

The word has also been used in different senses along with rhema. Both Plato and Aristotle used the term logos along with rhema to refer to sentences and propositions. It is primarily in this sense the term is also found in religion.