Instagram borrowed Snapchat's "Stories" format, but what makes it unique is how it works in concert with the rest of the photo-sharing app's features, Instagram COO Marne Levine explained at Fortune's Brainstorm Tech conference in Aspen.

"We've acknowledged over and over again that we did not invent the Stories format," said Levine. "It's a great format and it works well in our community," adding that Stories lets users post photos they often wouldn't post as traditional Instagram photos.

Why it matters: Instagram's decision to launch a feature identical to Snapchat's Stories last August has been met with both criticism and praise for getting its users to adopt it so quickly (currently 250 million people are using Instagram's Stories every day). The competition between the two apps is well known, and Stories has become the new battleground.