A spoken word or specific utterance — more concrete than logos. 'Man shall not live by bread alone but by every rhema that comes from the mouth of God' (Matt 4:4). Faith comes by hearing, and hearing by the rhema of Christ (Rom 10:17).
While logos can refer to reason and message broadly, rhema emphasizes the specific spoken word. The rhema of God is alive — breathed out (theopneustos) and active in ways that accomplish divine purpose.
Ephesians 6:17's 'sword of the Spirit' is the rhema of God — the specific, spoken, situational word applied to the moment. Paul pairs it with prayer (6:18), suggesting the Spirit supplies the right word at the right time.