Facebook-owned Instagram recently announced that its monthly active users have reached 300 million. This may sound like a staggering number, but Twitter co-founder Evan Williams is not impressed. In a report by Fortune, he explained that user count is not the right metric to use.

He said, "...'What is a [monthly active user]?' I believe it's the case that if you use Facebook Connect — if you use an app that you logged into with Facebook Connect — you're considered a Facebook user whether or not you ever launched the Facebook app or went to Facebook.com."

Facebook acquired Instagram for $1 billion in April 2012, and the latter likely uses the same metric for counting its users.

According to an SEC filing as noted by Fortune, Facebook uses MAUs to determine the size of its active user community worldwide. The company defines a monthly active user as someone with an account in the social networking site and is logged in, who, within the past month, has either visited the site, used the Messenger application, or shared content or activity with FB friends through a third-party app or website. Thus, whether or not a user has visited or used Facebook in the past 30 days, if they have clicked on "Like" or "Share" on a website, then they are counted as an active user.

"So what does that mean?" Williams added. "It's become so abstract to be meaningless. Something you did caused some data in their servers to be recorded for the month. So I think we're on the wrong path."

In a November report, the same online publication said that Twitter has 284 million monthly active users, a number that photo-sharing site Instagram has already surpassed. But that number does not include the microblogging site's logged out users and those who see tweets in websites. If Twitter's overall audience — or those users that, according to Twitter CFO Anthony Noto, "already exist on our platform" — is to be taken into account, the site would have an audience of around 500 million.

"Twitter is what we wanted it to be," Williams explained. "It's this realtime information network where everything in the world that happens on Twitter — important stuff breaks on Twitter and world leaders have conversations on Twitter. If that's happening, I frankly don't give a sh*t if Instagram has more people looking at pretty pictures."