Khvarenah, in New Persian Farr, is a mystical radiant force emanating from men chosen by God that confers upon them both divine right of kings and the cosmic capacity to do so justly.

Farr is understood as a real presence: an invisible yet palpable aura of righteousness that legitimizes rule, enables victory, and proves divine favor. A king possesses the Farr when his rule aligns with asha ('cosmic truth/order'); he loses it the moment druj ('the Lie', more generally, pride, cruelty, or falsehood) enter his heart. It is one of the most ancient concepts in Iranian civilization, attested long before the establishment of the Achaemenid Empire;

The Khvarenah of the Kiani,
Khvarenah that divinities and mortals alike should strive for.

— Yasht 19, Avesta; holy scripture of Zoroastrianism

The idea continues to dominate Iranian debates about just leadership to this day. While the Iranian Revolution nominally positioned itself against absolute monarchy, supporters of Ruhollah Khomeini "drew upon the concept of Farr. The Ayatollah specifically relied on the Iranian penchant for a supreme monarch endowed with a divine right to rule when he converted Iran's Islamic clerics into a new monarchical dynasty, with absolute power."

Avestan khvarenah is probably derived from Proto-Avestan *hvar "to shine", nominalized with the -nah suffix. Proto-Avestan *hvar is in turn related to Old Indic svar with the same meaning, and together descending from Proto-Indo-Iranian *súHr̥ "to shine", ultimately from Proto-Indo-European *sóhr "to shine". Other proposals suggest a linguistic relationship with Avestan xᵛar- "to eat".

Of the numerous Iranian languages in which the word is attested, the initial xᵛ- is evident only as Avestan khvar(e)nah and as Zoroastrian Middle Persian khwarrah, from which New Persian khorra then derives. In other Iranian dialects the word has an f- form, for instance as Median and Old Persian farnah-, from which Middle- and New Persian farr(ah) and adjectival farrokh derive. For many decades, the f- form was believed to represent a specific Median sound-law change of proto-Iranian xᵛ- to f-. The hypothesis has since been shown to be untenable, and the proto-Iranian form is today reconstructed as *hu̯, preserved in Avestan as xᵛ- and dissimilated as f- in other Iranian dialects.

Pre-Christian Georgian kings of the Pharnavazid dynasty were divinely assigned kxwarrah and its loss usually led to the monarch's imminent death or overthrow in Georgian kingship. Many of the monarchs had names based on this etymological root like Pharnavaz, Pharnajom and Pharasmanes. The word was borrowed into the Georgian language as p'ar[n].