"Mashallah" or "Mash'Allah" is an Arabic phrase used to show appreciation for a person or happening. It shows respect, and also reminds that everything is achieved by the will of God. The closest English translation is "God willed it." It is used to show joy and praise, and is evoked upon hearing good news.
The phrase has found its way into the language of non-Arabs, including Turks and peoples of the Balkans, including some who are not of the Islamic faith.
A: I just got an A+ on my exam.