Random variables are usually denoted by capital letters, X, Y etc and can be discrete or continuous. Let the r.v. X be the number of seeds germinating from 100. Let the r.v.
X be the maximum daily temperature in Newcastle.
Let X be response to question with 'Yes', 'No', 'Don't know'. X is not a r.v. Let Y be number of 'Yes's. Y is discrete r.v. Probability Distribution of a Discrete r.v.