The capital Latin letter Y.
A probability distribution is a function that describes the likeliness of a random variable to take on different values.
The Latin Alphabet is a collection of 26 symbols that form the basis of the English language. The alphabet's symbols are used throughout mathematics to represent variables, constants, and coeffecients.
The latin letter y is used to represent a variable or coefficient. Most commonly, y is the vertical dimension in the 2D cartesian coordinate system.