Tawbah is repentance, and the word means a turning. What is distinctive in the Qur'anic usage is that the same root is used of both parties: the servant turns to God, and God is al-Tawwab, the one who turns toward, who relents and accepts. The relation is stated at 9:118, where God turns to those who had failed "so that they might turn", divine acceptance both precedes and answers the human movement, a structure the theologians used when discussing the relation of grace and act.
The conditions are set out consistently by jurists and moralists: regret for what was done, desisting from it, firm resolve not to return, and, where another person has been wronged, restitution or the seeking of their pardon, since wrongs against people are not held to be discharged by God's forgiveness of the offence against himself. The door is described as open until death is actually upon a person (4:17-18) or, in a widely reported hadith, until the sun rises in the west.
Islam has no institution of confession to an intermediary, and no absolution pronounced by another. Tawbah is direct, and the tradition actively discourages publicising one's own sins, treating concealment as the ordinary rule and disclosure as itself a fault. The Qur'an couples the demand with repeated assurance, "do not despair of the mercy of God; God forgives all sins" (39:53), and the ninth chapter is named al-Tawbah, Repentance. Jewish teshuvah and Christian penitence share the underlying structure of turning and are treated comparatively in the entry on Repentance; the differences lie less in the requirement than in what mediates it.