Since you are Christian and the biblical definition of atheist is
"
Psalms 14:1 The fool has said in his heart, There is no God. They are corrupt, they have done abominable works, there is none that does good."
that as what I expect you to believe about atheists. But I assure you many atheists don't want to be associated with this definition for obvious reasons,
despite what some atheists here claim. Most atheists just live their lives without thinking much about God at all and they most certainly don't go around declaring that "There is no God". They don't want to be associated with a definition that calls them fools and corrupt etc and are trying to get rid of that stigma. Unfortunately, there are still people who insist on using this definition to the detriment of all weak atheists. I would encourage you to think of atheists simply as people who just live their ordinary normal lives without thinking about God with no firm opinions about him because he just doesn't matter to them.