The metric that continues to really impress me about Facebook: 58% of users log in each day (that's 526mm DAU out of 901mm MAU, according to its SEC filing). That's roughly the same percentage as it was in 2007, when I first heard that kind of stat.
I love customer surveys, but I don't think people are good at estimating how they actually spend their time or how frequently they do things.
Daily Active Users (DAUs). We define a daily active user as a registered Facebook user who logged in and visited Facebook through our website or a mobile device, or took an action to share content or activity with his or her Facebook friends or connections via a third-party website that is integrated with Facebook, on a given day. We view DAUs, and DAUs as a percentage of MAUs, as measures of user engagement.
When I first heard the stat, it was before FB Connect and Like Buttons had launched, and it seems to remain consistent today. The data seems to suggest that most users who use Facebook Connect or Like buttons will also visit Facebook.com (web or mobile) that same day. They do have a note saying that there may be mobile applications that drive daily activity automatically without active user intervention, and it may impact their measurement by up to 5%.
He's not asking what the acronymn stands for; he's asking whether it counts as a 'use' if you use Facebook to login to a third party site, or hit a like button, but you don't visit Facebook itself that day.
I love customer surveys, but I don't think people are good at estimating how they actually spend their time or how frequently they do things.