Zimbabwe's flag was adopted on April 18, 1980, the day the country became independent of Britain, and it has not changed since.
From Rhodesia to Zimbabwe
The region was Southern Rhodesia under colonial rule and later just Rhodesia. The flags of that period drew on British heraldry and stood for minority rule. Replacing them was the point of the new design, which broke with the older imagery entirely and drew its colors and symbols from the country's African population and the struggle they had fought.
The bird, the star and the seven stripes
Seven horizontal stripes run across the flag: green, yellow, red, black, red, yellow, green. Green is for vegetation and farmland, yellow for the country's mineral wealth including gold, red for the blood shed during the liberation struggle, and black for the heritage and identity of the African population.
At the hoist, a white triangle stands for peace. Inside it is a red star, which represents internationalism and the socialist aspirations that shaped policy after independence, and on the star sits the Zimbabwe Bird. The bird is taken from the soapstone sculptures found in the ruins at Great Zimbabwe, and it links the modern state to the ancient kingdom there.
Green, yellow, red, and black are Pan-African colors and appear on a good many other flags on the continent. The bird and the star are what make this one unmistakable.
Where the flag is flown
The flag flies over government buildings and military facilities and at national events, hoisted at sunrise and lowered at sunset under a fairly strict protocol. It represents Zimbabwe at the United Nations and at other diplomatic gatherings, and it is a fixture at sporting events, at home and among Zimbabweans abroad.
References
[1] Government of Zimbabwe Official Portal - www.zim.gov.zw
[2] Vexillology Enthusiasts' Website - "Flags of Zimbabwe," Vexilla Mundi. - www.vexilla-mundi.com
[3] National Archives of Zimbabwe - Collection of Rhodesian and Zimbabwean Flags.