On a TI-84, when using PoissonPDF(lambda, x) to compute P(X = x) for a Poisson distribution, what do the two inputs lambda and x represent?

Lambda is the sample size (number of trials); x is the probability of success per trial—the inputs are reversed from binomial syntax.

Lambda is the distribution's mean rate of occurrences for the fixed interval; x is the specific count value at which we want the exact probability.

Lambda is the cumulative probability up to x and x is the number of subintervals used to divide the main interval before computing the rate.

Lambda is the standard deviation of the Poisson distribution; x is the z-score transformed count value used for normal approximation estimates.