Badr was a watering place and stopping point near the Red Sea coast, about 120 km (in a straight line) south-west of Medina. In the second year after the Hijra (624 CE, during Ramadan) the first major battle between the Muslims and the Meccan polytheists took place here. Al Imran 3:123 names it directly: "Allah had already given you victory at Badr while you were weak."
Much of Surat al-Anfal concerns this battle: 8:42 describes the two armies' positions on either side of the valley, and 8:41 calls it "the Day of the Criterion" (Yawm al-Furqan), the day that separated truth from falsehood.
Today Badr is a town of the same name in Saudi Arabia; the battlefield and the cemetery of the martyrs of Badr lie close to it.