In the Old Testament, the main Hebrew term translated in English as "confess" is "yādâh", and its verbal stems add a rich and nuanced meaning to the Hebrew concept of "confess."

Yādâh (with the hiphil verbal stem)

Yādâh means to give thanks in the context of praise for or giving glory to God's majesty and power, gracious goodness, physical salvation from enemies or answered prayer. For example: a glorifying confession of the name of the Lord.

Yādâh (with the hithpael verbal stem)

Yādâh means to confess in the context of acknowledging sin and to give thanks.

The most common use of "yādâh" in the Old Testament is with the meaning of "giving thanks" and "praising" God:

And she conceived again and bore a son and said, "This time I will praise (yādâh) the LORD." Therefore she named him Judah. Then she stopped bearing. (Gen 29:35)

Therefore I will give (yādâh) thanks (yādâh) to You, O LORD, among the nations, And I will sing praises to Your name. (2 Sam 22:50.)

Without identifying the verbal stems, the dual meaning of "yādâh" can be seen in the following examples where there is a glorifying confession of God's name linked with the acknowledgment of sin:

When Your people Israel are defeated before an enemy, because they have sinned against You, if they turn to You again and confess (yādâh) Your name and pray and make supplication to You in this house, then hear in heaven, and forgive the sin of Your people Israel, and bring them back to the land which You gave to their fathers. When the heavens are shut up and there is no rain, because they have sinned against You, and they pray toward this place and confess (yādâh) Your name and turn from their sin when You afflict them, then hear in heaven and forgive the sin of Your servants and of Your people Israel, indeed, teach them the good way in which they should walk. And send rain on Your land, which You have given Your people for an inheritance. (1 Kings 8:33-36)

Now on the twenty-fourth day of this month the sons of Israel assembled with fasting, in sackcloth and with dirt upon them. The descendants of Israel separated themselves from all foreigners, and stood and confessed (yādâh) their sins and the iniquities of their fathers. While they stood in their place, they read from the book of the law of the Lord their God for a fourth of the day; and for another fourth they confessed (yādâh) and worshiped the Lord their God. (Neh 9:1-3)

In similar manner, the act of confessing is associated with repentance as seen here with Daniel:

So I gave my attention to the Lord God to seek Him by prayer and supplications, with fasting, sackcloth and ashes. I prayed to the Lord my God and confessed (yādâh) and said, "Alas, O Lord, the great and awesome God, who keeps His covenant and lovingkindness for those who love Him and keep His commandments, we have sinned, committed iniquity, acted wickedly and rebelled, even turning aside from Your commandments and ordinances. Moreover, we have not listened to Your servants the prophets, who spoke in Your name to our kings, our princes, our fathers and all the people of the land. Righteousness belongs to You, O Lord, but to us open shame, as it is this day—to the men of Judah, the inhabitants of Jerusalem and all Israel, those who are nearby and those who are far away in all the countries to which You have driven them, because of their unfaithful deeds which they have committed against You. Open shame belongs to us, O Lord, to our kings, our princes and our fathers, because we have sinned against You. To the Lord our God belong compassion and forgiveness, for we have rebelled against Him; nor have we obeyed the voice of the Lord our God, to walk in His teachings which He set before us through His servants the prophets. Indeed all Israel has transgressed Your law and turned aside, not obeying Your voice; so the curse has been poured out on us, along with the oath which is written in the law of Moses the servant of God, for we have sinned against Him. Thus He has confirmed His words which He had spoken against us and against our rulers who ruled us, to bring on us great calamity; for under the whole heaven there has not been done anything like what was done to Jerusalem. As it is written in the law of Moses, all this calamity has come on us; yet we have not sought the favor of the Lord our God by turning from our iniquity and giving attention to Your truth. Therefore the Lord has kept the calamity in store and brought it on us; for the Lord our God is righteous with respect to all His deeds which He has done, but we have not obeyed His voice. And now, O Lord our God, who have brought Your people out of the land of Egypt with a mighty hand and have made a name for Yourself, as it is this day—we have sinned, we have been wicked. O Lord, in accordance with all Your righteous acts, let now Your anger and Your wrath turn away from Your city Jerusalem, Your holy mountain; for because of our sins and the iniquities of our fathers, Jerusalem and Your people have become a reproach to all those around us. So now, our God, listen to the prayer of Your servant and to his supplications, and for Your sake, O Lord, let Your face shine on Your desolate sanctuary. O my God, incline Your ear and hear! Open Your eyes and see our desolations and the city which is called by Your name; for we are not presenting our supplications before You on account of any merits of our own, but on account of Your great compassion. O Lord, hear! O Lord, forgive! O Lord, listen and take action! For Your own sake, O my God, do not delay, because Your city and Your people are called by Your name. Now while I was speaking and praying, and confessing (yādâh) my sin and the sin of my people Israel, and presenting my supplication before the LORD my God in behalf of the holy mountain of my God, (Dan 9:3-19)

In this example, Daniel confesses the sins of his people, humbles himself under God's judgment, confesses that God is right and prays that God would show mercy. In essence, genuine confession of sin is the verbal recognition of the error of one's sin against the holiness of God. The genuine change of mind, repentance, to obey God's way provides the relief from God's judgment.

In yādâh, the concept of confessing is intertwined with the acknowledgment of sin and praise and thanks for God's majesty and power. It reflects in part the idea that the privilege of confessing a sin in seeking forgiveness from a Holy God is in itself something worthy of praising.