What is the difference betwen .ipa and .app format in iOS?

iOS app formats

iOS supports next app formats:

.deb - Debian package. Since iOS is based on Darwin (BSD) Unix family it is *possible to run such Linux format. For example Cydia package manager uses .deb for sharing applications on jailbroked devices.

.app - during development when you build your application for simulator or real device the .app is generated. You can find it in Products group. Sometimes .app is used to share application thought iOS simulators^[About]

.ipa - iOS App Store Package for iOS devices. When you publish/distribute or download an app using App Store your operates .ipa files. This container includes .app and other metadata. Actially it is an archive with .app. And to create it you should Product -> Archive -> ...

Disclaimer: my answer comes completely from digging around the files themselves.

.apps are application bundles. They contain the executable file, an Info.plist file, an icon, a launch image, and some other application resources. Application bundles are the only ones that actually get installed onto your device.

.ipas are archives that contain .app bundles as well as some other files meant only for iTunes to use, for instance iTunesArtwork. They are how iTunes manages applications, and as far as I can tell have little to do with the applications themselves other than App Store information.

I haven't worked with Flash CS5's export to iPhone feature, but you should be able to just drag your .ipa file to iTunes and it'll appear in the Apps list.

And also is it possible to develop iphone application in Adobe flash professional cs5?

It is possible in the sense that your iPhone software won't crash permanently or something, but as phwd and David have said, your app will not make it to the App Store.