Conditional probability density function

The conditional probability density function describes the probability over a random variable given the value of another random variable in the system. This is typically denoted by P(x | y), which represents the probability density of x over the random variable X when the random variable Y has a value of y. When the value of y is constant, the function P(x | y) is a probability density function over x. When the value of x is constant, the function P(x | y) is a likelihood function over y.