Khwarāsān () was one of the four kusts (frontier regions) of the Sasanian Empire, formed during the reign of king Khosrow I (r. 531–579). Khwarasan was commanded by a spahbed from one of the seven Parthian clans. The appointed spahbed of the kust was given the title of aspbed.
The name Khwarasan is a combination of khwar (meaning "sun") and āsān (from āyān, literally meaning "to come" or "coming" or "about to come").
References
Khwarasan Wikipedia(Text) CC BY-SA