The story
From an essay by American computer scientist Robert Shostak, who simplified the computing problem in a hypothetical siege by the Byzantine Empire. In the siege, a group of Byzantine generals, without central command and physically separated, need to vote to determine whether all troops should besiege the fortress or withdraw. Faults are personified as traitors who could vote selectively and messengers who could fail to deliver votes or forge them.
Etymology from Wiktionary, CC BY-SA 4.0.