Linked from
The 15 pages that link to Geometric distribution, each with the reason it gives.
Bernoulli trialRelated: It uses repeated Bernoulli trials to model waiting until success.
Coupon collector's problemRelated: Each stage waits for a draw from one of the still-missing types.
Negative binomial distributionBroader topic: It is the special case requiring exactly one success.
St. Petersburg paradoxRelated: It models how many coin tosses occur before the lottery pays.