This article studies the terms which were used to describe apostasy and apostates in early Christian literature (1st - late 2nd century). These terms may indicate the authors' attitude towards apostates, how they differentiated between cases of apostasy, and how unforgivable this sin was considered to be. Our analysis covers the New Testament, the “Shepherd of Hermas”, the writings of Justin Martyr, and three hagiographic works: the “Martyrdom of Polycarp”, the “Letter of the Churches of Lyons and Vienna”, and the “Martyrdom of Pionius”. An analysis of these texts reveals that many authors drew a distinction between apostasy involving sacrifice to pagan gods or the emperor, and apostasy involving blasphemy and betrayal of Christians. While the former was considered a grave but venial sin, the latter was deemed completely unjustifiable. Similarly, consideration was given to whether the act was carried out voluntarily or under duress. Finally, the very possibility of forgiving apostates was an important issue. These differences prompted church authors to use various designations borrowed from the New Testament tradition to describe different categories of fallen ones, and to avoid the word 'apostasia', which denotes unforgivable apostasy.