Communicatio Idiomatum
“The communication of attributes.” Because Christ is one person in two natures, what belongs to the divine nature can be said of the man Jesus and what belongs to the human nature can be said of the Son of God: God was born, God suffered, God died. Lutherans press this further than most traditions, and it is why they can say Christ's body is genuinely present in the Supper.
In Doctrine — What Lutherans teach, and where it differs from neighbouring traditions.