الله أكبر
Allāhu akbar
“God is greater”: the phrase that opens the prayer and the call to prayer, and is said in many other moments of life.
What it means
It is said at the start of the prayer and between its movements, in the call to prayer, at Eid, at the slaughter of an animal for food, and in joy and in distress. “Greater” means greater than anything one might put in His place.
Often misunderstood as
That it is a battle cry.
What the sources say
Muslims say it at every moment of the day and far more often in prayer than anywhere else. Some Muslims also say it in battle, and violent groups have used it. That does not change its meaning, which a Muslim hears several times a day in the adhan.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 56, listed as ALLĀHU AKBAR.. The definition is restated here.