ajax is a term used for the technology that uses both server side scripts like php/asp/etc and client side scripts like javascript for the pages.
so for eg- a messenger app will interact with the server to send and receive messages and notifications, while the client side scripts will display this chat messages making it appear to the user that the page is live and does not have to reload itself to display the new data.
this means that apple is allowing these kind of live pages and also allowing pages that do not interact with the backend server at all, but they will only interact with the phone features. a page like this could be as simple as a url/bookmark for a live page, or it can be like an html page with embedded javascript saved on/downloaded to your phone.
now apple could do something cool like making these live pages or application pages appear like any other application on the phone by allowing us to add these pages/bookmarks to the applications menu on the phone with nice icons, this will make the users completely oblivious of the fact that these "applications" are not really applications as in an executable file, and make it a lot easier for the users. we will get our answer on the 29th i guess.