Jazāk Allāh (Arabic: جَزَاكَ ٱللَّٰهُ, ) or Jazāk Allāhu Khayran (Arabic: جَزَاكَ ٱللَّٰهُ خَيْرًا, ) is a term used as an Arabic expression of gratitude, meaning "May God reward you [with] goodness."
Although the common word for thanks is shukran (Arabic: شُكْرًا), Jazāk Allāh khayran is often used by Muslims instead.
The response to this phrase is wa ʾiyyāk(i) (Arabic: وَإِيَّاكَ), or wa ʾiyyākum (Arabic: وَإِيَّاكُمْ) for the plural, which means "and to you". A more formal reply is "wa ʾantum fajazākumu llāhu khayran" (Arabic: وَأَنْتُمْ فَجَزَاكُمُ ٱللَّٰهُ خَيْرًا) "And you too, may God reward you with goodness".