Hello.
Essentially, it's the same as any other AS 3.0 scripted flash project. It can be both AIR and webpage compatible. If you wish, I can upload a sample of my previous work for Adobe AIR.
What your client is requesting, by the looks of it, is that the web application is also usable as a desktop application, that's why they are asking for the AIR compatibility.
You might want to double check, however, what it is that they exactly want. As in "what it should DO", not "how it's made". Clients frequently get lost in the buzzwords and don't have a clear idea of what they need.
Hope I can be of help.
Alex.