Trial

Trials are the unit you count when you repeat a random process, and they are called independent when the result of one does not change the probabilities for the next. A simulation works by running many trials and tracking how often the event of interest shows up. Flip a coin 20 times and you have run 20 trials, each landing heads or tails; if 12 come up heads the relative frequency of heads is $12/20 = 0.60$. The binomial setting is defined by a fixed number of independent trials that each have the same probability of success.