What does apostasy mean in the context of Christianity?

In Christian theology, apostasy is viewed as a grave matter involving a deliberate rejection of Christ and the Gospel after previously having an understanding of or experience with them. This is explicitly addressed in Hebrews 6, where the author warns that those who fall away after tasting the heavenly gift cannot be renewed to repentance. Such a departure signifies that these individuals were not truly part of the faith community or genuinely regenerated, as true believers are eternally secured by God's grace and cannot ultimately apostatize.