Black Week is a phrase frequently used in the popular press to mark periods of a few days when a string of similar unfortunate events occur. Its celebrity usually fades to be replaced by another Black Week a few years later. However, a few Black Weeks have acquired an historical notoriety.

One of the periods which still retains the name was 10-15 December 1899, during the Second Boer War when the British Army suffered three humiliating defeats by the Boer Republics, at Magersfontein, Colenso and Stormberg .