An expression meaning ‘God is Greater (than can be described)’. This phrase is so important in Islamic worship that it has a title: takbīr

The takbīr is the opening phrase of the adhān (call to prayer), a portion of the tasbīḥ of Fāṭimah az-Zahrāʾ (ʿa), and it is an essential component of the ritual prayers. 

Muslims may also use this phrase in conversation to express joy, awe, relief, or gratitude.