But is this usage precise? What does this terminology really mean?

The notion that the Word of God is the Bible alone is erroneous, and finds its origin in the Protestant Reformation led by Martin Luther (who founded the Lutheran Church). Later on, the Reformation splintered in many directions and countless rival camps were born out of it. However, all the different denominations, though conflicting in beliefs and practices, followed the same doctrine that the Word of God is the Bible alone, and anything else outside of the Bible is not considered inspired.

Two sources

In accordance with the teachings of the Apostles, the Catholic Church teaches that the Word of God comes to us in two sources, namely: Sacred Scripture and Sacred Tradition.

The Catechism of the Catholic Church (CCC) explains that the Gospel was handed down in two ways: orally by the Apostles (who received instruction from Christ directly and also through inspiration by the Holy Spirit) and in writing by the Apostles and those associated with them, also under the inspiration of the Holy Spirit. The Apostles then conferred their teaching authority upon their successors, the bishops, who in turn conferred the authority upon their own successors, all the way down the ages. This “living transmission, accomplished in the Holy Spirit is called Tradition, since it is distinct from Sacred Scripture but closely connected to it.” Sacred Tradition, therefore, “perpetuates and transmits” the Church, its doctrine, life and worship.” (CCC 76-78)

The Catechism further explains the relationship between the two as follows:

(80) “Sacred Tradition and Sacred Scripture, then, are bound closely together, and communicate one with the other. For both of them, flowing out from the same divine well-spring, come together in some fashion to form one thing, and move towards the same goal.”

(81) “Sacred Scripture is the speech of God as it is put down in writing under the breath of the Holy Spirit.”

“and [Holy] Tradition transmits in its entirety the Word of God which has been entrusted to the apostles by Christ the Lord and the Holy Spirit. It transmits it to the successors of the apostles so that, enlightened by the Spirit of truth, they may faithfully preserve, expound and spread it abroad by their preaching.”

(82) As a result the Church, to whom the transmission and interpretation of Revelation is entrusted, “does not derive her certainty about all revealed truths from the holy Scriptures alone. Both Scripture and Tradition must be accepted and honoured with equal sentiments of devotion and reverence.”