Yeah, something that you've built that when it comes up in the interview, you're able to explain the goals you were trying to achieve, the trade-offs and design decisions, perhaps some A/B tests you've run and metrics you tracked.

Even if the app is simple and has a grand total of 2 users, it should provide decent conversation fodder and peg you as disciplined, detail-oriented and big-picture-focused. For example, if you have not built something obvious in (internationalization, in-app purchases, deep links), throw in an explanation of how you're aware of it and made sure it fits into the next release.

One quote from Sam Altman' startup class that stuck with me was (I believe it was from Brian Chesky) someone asking two builders what they were working on laying bricks. One said "I'm building this wall", another said "I'm building the cathedral". Be the second guy.