In Byzantine General's Problem a group of generals plans to attack a city from different parts, for the attack to be successful all the generals have to attack simultaneously.
The Generals coordinate their attack by communicating through messages. The messages passed between generals can get changed or altered by a treacherous general.
In Distributed systems, the generals are analogous to nodes and the treacherous generals are the malicious/corrupted node also known as Byzantine nodes.
Distributed systems like blockchains have to devise solutions to overcome this problem and become Byzantine fault-tolerant systems.
