A Christian from the bible stand point is someone who has taken part in the first resurrection
Revelation 20; 6 Blessed and holy are those who share in the first resurrection. The second death has no power over them, but they will be priests of God and of Christ and will reign with him for a thousand years.
~TW~
A Christian is someone who follows the teachings of Jesus.
Jesus never said anyone had to follow any of the existing sects or denominations existing today.
The bible, if it hints at anything, seems to make the point that ultimately it would be Jesus who decides who has been a "true" Christian or not, not a bunch of judgmental people.
Therefore who is a Christian isn't who
other people says it is, but who Jesus says it is.
Problem sorted.