Under the framework of covenant theology, Adam is considered as a "federal head" or representative of all of his progeny.
His sinful act of eating the fruit from the tree of the knowledge of good and evil which was forbidden by God had consequences for all humanity.
A person that has sin imputed to them becomes guilty of transgression before God for being in violation to his laws and is subject to his punishments in the life hereafter.
Under the "mediate imputation" view (due to Joshua Placaeus), humans inherited a proclivity to sin because of Adam's act.
[2] In recent years, theologians have begun to explain the transmission of original sin by socialization and character deformation rather than imputation.