What makes one a "born again Christian" as opposed to a Christian?

A born again Christian is one who does not start out as a religious individual, but at a point in his/her life, becomes considerably more religious, "rediscovering" his/her Christianity so to speak.

In Judaism the phenomenon occurs as well, and is known as "(c)hazarah bit'shuvah" ("returning [to God] on the [right] path").

The new birth is the act by which God imparts spiritual life to one who trusts Christ.Without this spiritual birth, a person cannot perceive spiritual things, nor can they enter the kingdom of God. (John 3:3)

https://www.desiringgod.org/messages/what-happens-in-the-new-birth-part-1

"Christian" is a widely used to describe people who express ANY kind of belief in Christ, no matter how vague their belief may be. They may or may not believe the Bible (Word of God) is the final word on religious things, but will take the word of a minister or priest, or of their own decision to be the last word. (Personally, I believe that if God, the one who Created by speaking, said it then it must be final).
A "born again Christian" typically believes that "salvation" has nothing to do with what we do anymore than we have somehow earned being born. "Born again" is an expression used by Christ (which means Messiah in Greek by the way and Jesus means Savior/salvation) when he was talking to Nicodemus "a man of the Pharisses, a ruler of the Jews" "Except a man be born again, he cannot see the kingdom of God." This is in John 3.