What’s the difference between is hatarat nedarim and hafarat nedarim? TB Nedarim 75

The Mishnah on daf TB Nedarim 75 brings a disagreement between Rabbi Eliezer and the sages whether a husband/father may proactively annul the wife’s/daughter’s vows. “If he states that all vows that she will take until then are hereby nullified, Rabbi Eliezer said: They are nullified, while the Rabbis say: They are not nullified.” (Sefaria.org translation)

In his commentary the Ron ד"ה דְּאַתְפֵּיס אַחֲרִינָא בְּהָדֵין נִדְרָא describes the fundamental difference between the two different kinds of annulments. The first method of annulment is hatarat nedarim (התרת נדרים). This annulment of a vow takes place in front of a Sage or rabbinic court. The person provides an explanation for wanting to annul the vow, and if the court finds sufficient justification (a petakh-פּתח) the court will cancel it. The second method of annulment is hafarat nedarim (הפרת נדרים). This annulment of a woman’s vow performed by her father (if she is still a minor or unmarried) or by her husband (if she is married) within a day of learning that she made it. Neither justify grounds for annulment for rabbinic presence is required.

Hatarat nedarim expunge his the vow from its very inception. It uproots it as if the vow never ever existed. Hafarat nedarim can never be retroactive. This method of annulling a vow may be used only from the time the vow was made and learned by the husband or father. In daf TB Nedarim 76 we shall learn what does the time limit “within a day” mean.