It is a term that is applied to anything that acts like a tool for the users, often with a webservice behind it providing the features, and often with a mobile phone version, but, you can get apps for windows8, chrome and other browsers, as well as for phones.
I have been describing this as an app for multiple platforms, which means one that works on desktops, tablets, and phones, and adapts to each type of platform so that it is most easily used for that. In fact, for the most complete use if it’s features, the app will encourage people to use it on a desktop as well, it will have a “send to my desk” function so a person can start an entry then store it for later improvement.
I am actually personally more focused on the conventional web desktop experience than the app, as I see that part of the project as the most critical. That’s where the real action happens, where the community engages; it’s the “mind” of the project, the apps in the phones are the senses, bringing in streams of messages and information, and receiving suggestions from the “mind”.