I'm currently learning binomial random variable on Khan academy and in one of the video, Sal said that in order for a random variable to qualify as a binomial random variable, it has to meet four conditions
1) the outcome of each trail can be classified as success or failure
2) each trail is independent of each other
3) there is a fixed number of trails
4) the probability of success on each trail is constant
Could someone please explain the logic behind point 3? Why is fixed number of trail a requirement for random variable to qualify as a binomial random variable?