At first the term sounds odd but shouldn't. Jesus and in fact all of the authors of the new testament use a variety of images taken from ordinary life to try and express the mysteries that are the Christian faith.
Throughout the history of Christianity different groups have chosen to focus on specific one without denying the power of the others. The Second Vatican Council, whose 50th anniversary we are about to celebrate, chose the People of God and the Body of Christ as focal points to describe the Church.
We tend in the 21st century to think Evangelical Christians when we hear the term "born-again." In fact, the term is equally applicable to other Christians including Catholics.
As we see in today's gospel it comes from the third chapter of John and his conversation with Nicodemus. It is a classic example from John's gospel where practically everything has at least two meanings.
The word translated "again" in the phrase "born again", can also be translated "from above." The phrase has a double meaning one must be "born again" or "born from above." This double meaning is what sets up the confusion of Nicodemus
"How can a man once grown old be born again? Surely he cannot reenter his mother's womb and be born again, can he?"
And the opportunity for Jesus to explain that what he is referring to is birth by "water and Spirit" , the Holy Spirit which comes from above.
The rebirth to which Jesus refers is the rebirth we have all experienced in Baptism. Every baptized Christian is a born-again Christian. And we are called to live not out old life, but the new life we received from above.