The term 'Eight Letter of the Greek Alphabet' refers to the eighth letter of the Greek alphabet, Theta (Θ). Theta is a consonant and is pronounced as a 'th' sound. It is used in many words, such as 'THEORY' and 'THEOLOGY'. In mathematics, Theta is often used to represent an angle or a rotation. In physics, it is used to represent a wave function. In chemistry, it is used to represent a bond angle. In finance, it is used to represent the rate of change in option prices.