C. F. Keil and Franz Delitzsch on 2 Chronicles 20:5

2Ch 20:5

When the inhabitants of Judah and Jerusalem had assembled themselves in the house of God, Jehoshaphat came forth before the new court and made supplication in fervent prayer to the Lord. The new court is the outer or great court of the temple, which Solomon had built (2Ch 4:9). It is here called the new court, probably because it had been restored or extended under Jehoshaphat or Asa. This court was the place where the congregation assembled before God in the sanctuary. Jehoshaphat placed himself before it, i.e., at the entrance into the court of the priests, so that the congregation stood opposite to him.