A Christian ( pronunciation (help·info)) is a person who adheres to Christianity, an Abrahamic, monotheistic religion based on the life and teachings of Jesus Christ. "Christian" derives from the Koine Greek word Christós (Χριστός), a translation of the Biblical Hebrew term mashiach. 

There are diverse interpretations of Christianity which sometimes conflict. However, "Whatever else they might disagree about, Christians are at least united in believing that Jesus has a unique significance." The term "Christian" is also used adjectivally to describe anything associated with Christianity, or in a proverbial sense "all that is noble, and good, and Christ-like." It is also used as a label to identify people who associate with the cultural aspects of Christianity, irrespective of personal religious beliefs or practices. 

According to a 2011 Pew Research Center survey, there were 2.2 billion Christians around the world in 2010, up from about 600 million in 1910. By 2050, the Christian population is expected to exceed 3 billion. According to a 2012 Pew Research Center survey Christianity will remain the world's largest religion in 2050, if current trends continue.
Which culture is the word derived from?
Koine Greek