Startup versus fun or useful application

It seems like "startup" is a term whose meaning is getting fairly broad on this site. Both of these front-page submissions were advertised as "startups":

http://news.ycombinator.com/item?id=456471

http://news.ycombinator.com/item?id=456503

When does an online application become a startup? Is this just a semantic distinction, or is there something more to it?