So … API. Have you heard the term used enough? Chances are, if you follow Twitter, it’s growth or are a developer of any kind, the answer is a resounding, YES.

For those that haven’t, API stands for application programming interfaces, which enable programs to access features of other applications. Name your favorite, Tweetie, TweetDeck, TwitterBerry, the list is endless. According to a post from The Guardian, only 20% of traffic comes through Twitter.com, the remaining 80% comes from various API through computers and smart phones. In early June, during The D Conference: All Things Digital, founders Biz Stone and Evan Williams were interviewed by Walt Mossberg and Kara Swisher about where Twitter might be heading. When talking about API, Stone and Williams commented that while they’re working to make their user interface as good as possible, they welcome the dozens of companies and enthusiasts providing added value toward the best Twitter experience possible. Openness and personal experience are two cornerstone themes of the company and the variety of API demonstrate that in a very profound way.

With all the conversation about twitter followings and influence, it’s interesting to learn straight from Evan Weaver, Twitter’s Lead Engineer on the Service Team, that the average user has 126 followers. Now, with any average, the extremes exist (i.e. the silent accounts that are there to simply listen and the Chris Brogan’s who have more followers than God) but I would argue that this average makes a strong statement for the growing mainstream popularity of Twitter. Based on this average, people aren’t jumping into Twitter with the intention of reaching thousands of people. Instead, they’re there to connect, talk and maybe make some connections that they wouldn’t be able to otherwise.

What do you think? Is API eclipsing the Twitter brand? Which API could you not live without? Is Twitter actually mainstream or just hype in the media? Let us know.