Susan won 2000 at the blackjack tables on her birthday her winnings are an example of?

...a successful trip to the casino.

Without knowing anything about her play (whether she is just a "plopper" or random chance gambler, or an advantage player), it is impossible to determine whether her winnings are an example of luck, skill, or any meaningful combination of the two.

EDIT: I didn't see that this was in "school subjects: math." To give you the math term you're looking for, we would need some information about what you are studying specifically.