Plato's 'B' is the Greek letter BETA, which is the second letter of the Greek alphabet. It is often used to represent the number two in mathematics and science. Plato was a philosopher from ancient Greece who wrote extensively on topics such as ethics, politics, and metaphysics. He is widely considered to be one of the most influential thinkers in Western philosophy. The term 'Plato's B' is often used to refer to his works, particularly those written in the form of dialogues.