It's Traditional! With a big "T".

 Sacred Tradition is as the Catechism of the Catholic Church defines in CCC 81 is the transmission of the Word of God as was entrusted to the Apostles by Our Lord Jesus Christ and the Holy Spirit. The transmission of Sacred Tradition is the means by which the Faith was spread through out all of the known world prior to the writing of inspired, and canonical, New Testament Scriptures. Many of the New Testament Scriptures refer to Traditions and how they are used to pass on the Traditions in 2 Thessalonians 2:14, John 21:25, 2 John 1:12, and 1 Corinthians 11:2. Surely if we refer to Scripture as a defense (not the only defense) of Sacred Tradition, then that would indicate the primacy of Scripture right? Well, in short, no. Let's talk about why. 

First, Tradition is what was handed down orally by the Apostles. The bible as we know it did not exist during their lifetime, c.f., It's a Cannon, and all we had was the Teaching Church established by Jesus Christ, with St. Peter as the First Pope, or First Among Equals one of the terms by which St. Peter is singled out due to the honor placed on him by Christ. It is by this oral tradition that we know of the Last Supper and the Eucharist. It is by this oral tradition that the Good News (Gospel) of the Ministry, Sacrificial Death (Passion and Crucifixion), and Resurrection was spread. It is by this oral tradition that the Catholic Church was able to compile the New Testament and added to the Septuagint to form the canon of Scripture that is the Holy Bible. 

Where can we see this oral tradition written down? In the writings of the Church Doctors and Fathers. The Church Fathers and Doctors (to an extent) were either direct disciples of the Apostles, contemporaries of the Apostles, or disciples to the disciples of the Apostles. In fact, much of the New Testament was written by the Apostles disciples. A majority of the Pauline Epistles were written by St. Luke, the writer of the third Gospel account. This Sacred Tradition can also be found in the Papal Decrees, Church Councils, and the Liturgy of the Church found in the missals (the book in which we have the readings of the Mass).  

Why did I mention at the beginning that it is Tradition with a big "T"? Well to separate the Sacred Tradition from the historical tradition. One is handed down from God, i.e., Jesus Christ to His Apostles, and the other is handed down from culture to culture, society to society, nation to nation, generation to generation. Just as the Church established by Christ is Holy, so is the Tradition He handed down. Sacred Tradition, protected by the Holy Ghost from manipulation or error, is one of the three guiding factors in the Church. The other two are Sacred Scripture, formed by Sacred Tradition and taught by the Magisterium, and the third is the Magisterium itself. 

The Magisterium is the teaching office of the Church, originally held by the Apostles during the early Church, and now it is held by the successors of the Apostles, the Bishops. This succession is called Apostolic Succession and is first demonstrated in the Book of Acts when the Apostles elevate Matthias to the office left empty by the betrayal and death of Judas Iscariot. The combination of the three, Sacred Tradition, Sacred Scripture, and the Magisterium form the Authority of the Church. It is this Authority that the Church teaches, guides and instructs the masses to follow Christ through the Church established by Him on St. Peter.