random variable
assumes any of several different numeric values as a result of some random event
discrete random variable
a random variable that can take one of a finite number of distinct outcomes
continuous random variable
a random variable that can take any numeric value within a range of values
probability model
is a function that associates a probability P with each value of a discrete random variable X, or with any interval of values of a continuous random variable
expected value
is a random variable's theoretical long-run average value, the center of its model
variance
is a random variable's expected value of the squared deviation from the mean
standard deviation
describes the spread in the model, and is the square root of the variance of a random variable