What letter does 'Ψ' stand for in the Greek alphabet?

The letter 'Ψ' stands for "Psi" in the Greek alphabet. In the context of the Greek letters, "Psi" is the 23rd letter and is typically associated with various concepts in mathematics and science, often symbolizing wave functions in quantum mechanics and representing psychological phenomena in various psychological theories.

In Greek, each letter has a distinct sound and numerical value, and "Psi" is pronounced like "sigh" with a "p" sound at the beginning, which can often lead to confusion with similar-looking letters. The letters "Chi," "Phi," and "Rho" represent different sounds and positions in the Greek alphabet, which highlights the unique identification of "Psi" as 'Ψ'. So, identifying 'Ψ' as "Psi" reflects an understanding of the Greek alphabet and its significance in various academic fields, making it the correct answer.