What do you call people who used to believe in god but turned away?

What do you mean by 'turned away'?

If you mean they still believe in a God, but stopped practicing a religion to worship it, then they are still theists. They're just non-religious, or apostates of their old religion.

If they stopped believing in Gods altogether, they didn't 'turn away'-- no more than you 'turn away' from the tooth fairy when you discover it doesn't exist. They are are called atheists.

We are called "atheists". I wouldn't call it "turned away" though. We lose our beliefs when we realize the state of the world and universe are not compatible with an all-perfect God, or that there is not enough evidence to justify the extraordinary God claim.

For some people, it's an epiphany. For others, it's a long process that can take months, years, even decades. Childhood indoctrination can be very difficult to overcome.

Thanks for asking.

The bible calls them "backsliders".

A backslider in the Bible is a person who once had salvation, but has since turned away from the Lord Jesus to the point that he is now spiritually lost and dead again, just like he was before becoming saved.

But those who turn to crooked ways the LORD will banish with the evildoers. (Psalms 125:5)

But God is so merciful and says in Jeremiah 3: 14 Turn, O backsliding children, saith the LORD; for I am married unto you: and I will take you one of a city, and two of a family, and I will bring you to Zion:

The Lord doesn't give up on his children, just like a earthly father would not give up on his son/daughter if they walk in the wrong path of life. God wants the best for us, and he has his best interest for our lives, but we are the disobedient ones and think we don't need God. But when we depart from him, his presence also departs from us, and that's when temptations comes in and makes us do terrible things to ourselves and others. But if you walk with God and hold on to his truths, then no weapon formed against you shall prosper, nor evil devices will come on your way, for greater is he that is in you, than he that is in the world, and if God is for us, who can be against us? no one.

agnostics or heathens, or atheists etc.

there are different types of people who turn away, not all just lose belief in God, they actually still question him.

maybe those as referred to above don't actually turn away from God but rather the thwarted image of Him as scripted in religion.

Re-educated.

No longer God believers.

Intelligent.

Geniuses.

The seekers who finally found truth.

BACK SLIDERS

God promises to remarry them (Spiritually though).