this is a good question that deserves just as good of an answer.
The passage from the Bible that answers this question is John 3:1-21. The Lord Jesus Christ is talking to Nicodemus, a prominent Pharisee, and member of the Sanhedrin (a ruler of the Jews). Nicodemus had come to Jesus at night. Nicodemus had questions to ask Jesus.
As Jesus talked with Nicodemus, He said "...Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God." Nicodemus said to Him, "How can a man be born when he is old? Can he enter a second time into his mother's womb and be born?" Jesus answered, "Most assuredly, I say to you unless one is born of water and the Spirit, he cannot enter the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. Do not marvel that I said to you, You must be born again...." (John 3:3-7).
The phrase "born again" literally means "born from above." Nicodemus had a real need. He needed a change of his heart--a spiritual transformation. New birth, being born again, is an act of God whereby eternal life is imparted to the person who believes. John 1:12,13 indicates that "born again" also carries the idea "to become children of God" through trust in the name of Jesus Christ.