Niger's flag is the African national flag traditionally given a conventional 6:7 proportion. That makes it unusually close to square compared with the more familiar 2:3 or 1:2 formats used by many national flags.
The flag is a horizontal orange, white, and green tricolour with an orange circle in the center. It was designed in 1958 and adopted on 23 November 1959, while Niger was still part of the French Community. The design remained in use when Niger became independent in 1960.
The 6:7 ratio is best treated as a traditional convention rather than an unambiguous legal requirement. Niger's Constitution does not explicitly specify the ratio, and government or printed examples have not always used it consistently. That qualification is why the question says “conventional.”
The colors are commonly interpreted geographically: orange for the Sahara, white for the Sahel, and green for the fertile south. The orange disc is generally understood as representing the sun, though some symbolic explanations are not officially confirmed.