The term 'A Greek Letter' can be solved by the three letter word 'TAU'. TAU is the 19th letter of the Greek alphabet and is written as Τ in uppercase and τ in lowercase. It is pronounced as 'taf' and has a numerical value of 300. In Ancient Greek, it was used to represent a cross or a crucifix. In modern times, it is often used to represent a variety of concepts such as life, strength, and endurance.