An API is a set of functions and essentially a programming language (and it use that term very loosely!) that allow third party developers to develop applications and websites that interact with them.
Facebook has a similar API for it’s own service, unsurprisingly called, yep, you guessed it, Facebook API.
Now with the Facebook API you can (as long as you have sufficient permissions from the user) access profile information, friends lists wall posts, about me, work history and a great deal more information and use this to enhance the experience for Facebook users on your own website. You can even post to their wall, update their status, share photos and videos etc.
Now the reason why the Google+ API (based on OpenSocial – a popular open source social networking platform) is frustrating developers? Well, if you want information, such as the profile information, ‘circles’ information etc you’re fine. But a lot of data from your Google+ site cannot currently be shared. The major thing however is that communication with the Google+ API is pretty much all one way. You can get information from it, but cannot send (for example update status posts, add new photos etc) back to it currently.
Now Google+ is based, and is largely composed of OpenSocial – which has all these functions in place. But Google+ has it’s own special variant of OpenSocial and currently hasn’t released any functions to send information to Google+ or even got all the functions to retrieve all the information from Google+, if authorised.
Until Google+ does this it is unlikely to see as rapid growth in app development on it’s platform as Facebook – who has new websites and apps appearing everyday that integrate the worlds biggest social network.
No doubt it is in the plans of Google to release a fully functioning and comprehensive API but we hope this is in the near future. Every day that it is not released they are likely to fall even further away from Facebook, who already have, without doubt, the commanding share of the social networking market.