المعنى الاصطلاحي :

A person whom the judge relies upon and refers to in order to determine the reliability of a witness.

الشرح المختصر :

The "muzakki" (investigator of witness reliability) is someone who is used by the judge to verify the credibility and reliability of witnesses. "Tazkiyah" (verification of reliability) is of two types: 1. "Tazkiyat-us-sirr" (secret verification of reliability): When the judge chooses a trustworthy and pious person to investigate the reliability of a witness. This person then asks those who are close to the witness, such as his neighbors and peers. 2. "Tazkiyat al-‘alāniyah" (public verification of reliability): This occurs after the judge has already completed the secret verification. The judge brings forth the person who testified to the reliability of the witness and asks him to publicly testify that the witness is an upright person who prays, fasts, does not engage in false testimony, is not one who lies in his speech, etc.

التعريف اللغوي المختصر :

"Muzakki": person who testifies to the goodness of others and ascribes "zakā’", meaning righteousness and uprightness, to them. Other meanings: one who purifies and amends; a person who praises and testifies to someone's trustworthiness.