The term 'It's Between Eta and Iota' is referring to the Greek letter Theta, which is the 8th letter of the Greek alphabet. It is located between Eta (7th letter) and Iota (9th letter). Theta is often used in mathematics and science to represent an unknown variable or quantity. In physics, it is used to represent angular displacement, while in mathematics it is used to represent a variety of concepts such as angles, complex numbers, and even probability distributions.