Verbum caro is Latin and a reference to the Latin text of John 1:14, the Word was made flesh (et Verbum caro factum est). It refers to the Incarnation, God's taking on of humanity in Christ.
Hans Urs von Balthasar uses the phrase, for example, in Theo-Drama volume 4, page 104: "Man is not able to anticipate the synthesis of the Verbum-caro …" Hans Urs von Balthasar. The Dramatis Personae: Man in God. Translated by Graham Harrison. Vol. 2 of Theo-Drama: Theological Dramatic Theory. San Francisco: Ignatius Press, 1990.