Linguistic Definition of Tawbah:

Tawbah in language is the infinitive of (تاب) which means “to return.” It is derived from the root meaning “to return, to come back, to regret and feel remorse.”

Technical Definition of Tawbah:

It means that I should acknowledge my sins and wrongdoings, and after regret and remorse for them, resolve never to return to such sins again. And I should correct my past conduct through good deeds, and intend to reform through actions whose correction is possible through deeds. And for Allah, I should purify my intention while doing this, with the hope of reward and fear of punishment, abandoning negligence in fulfilling obligations. This is conditional that it should be done before gharghara (غرغرہ) (the time when the soul reaches the throat) and before the sun rises from the west.

(1) Gharghara refers to when the soul is in the throat at the time of death, meaning when death is near and a person can see the angels.