Heresy, schism, and apostasy are related but distinct concepts in Christian theology and canon law.
Heresy
Heresy is the obstinate denial or distortion of a truth that belongs to the Christian faith. Historical use of the term requires precision: disagreement, error, or unfamiliar terminology is not automatically formal heresy.
Schism
Schism is a rupture of ecclesiastical communion or refusal of legitimate ecclesial unity, even where the parties may profess much of the same doctrine.
Apostasy
Apostasy is the repudiation or abandonment of the Christian faith as a whole. Pastoral judgment distinguishes a person’s objective act from questions of knowledge, freedom, culpability, and reconciliation.