Khorram Rooz (Persian: خرم روز xoram rūz) is the first day of Dey, the 10th month of the Iranian calendar.
(Persian New Year is on the First day of the Spring in Iranian Calendar.)
In Persian, "Khorram Rooz" translates to "happy day".
The Muslim scholar Abū Rayḥān al-Bīrūnī wrote that the month Dey is also called khor.
The Zoroastrians call it dey dadar jashn.