1) Refers to XXX-rated live stage female performers ("ponies") that will use only one stallion as a sex partner for all performances.
2) When said, it is a jab at Joe Biden not knowing the correct saying of "one TRICK pony" when he snapped at a reporter that was tenaciously asking questions about his son Hunter's alleged wrong doings with regard to international financial transactions.
"I don't know what she's going to do when they put that stallion out to stud!" LOL
"C'mon man! You're a one horse pony on that question, I'll give you that!"
The worthiness of a digital application (apps) for one user to share with another, with interaction between users mandatory for functionality of the app or one of its features. Different from virality, where one user simply passes on information from one source to another user with no interaction required between users whatsoever (sharing a link or image, etc.), however, both measure success with higher numbers from simple seeding(one user shares with others and those new users share with even more, newer users, and so on).
The "sharability" factor of that sports app, SpeedBrackets, is huge, because it requires users to form their own contests with their friends and families, co-workers, and even customers for business owners.