Aruba Instant refers to deployments of Aruba enterprise access points without physical controllers (running Aruba Instant code), whereas controller-based deployments run ArubaOS (AOS). Historically we used to offer different access point variants for these deployments: same physical AP hardware, but loaded with different code; Instant APs (IAP) running Instant code, and controller based APs running AOS. So the IAP-225 and AP-225 share the same hardware family (and belong to the same 220 Series product line), but strictly speaking those are different products. Both of these (as well as the entire 220 Series) have been EOS for some time. As you can see in the notice, it covers both.
In more recent AP platforms, we've combined both deployment models, and the same product can be used either with a controller (running AOS) or without a controller (running Instant), and it is relatively easy to transition between the two.
In the title of this thread you mention "InstantOn". That is a completely different product line, focusing explicitly on SMB. Different products, different code, and not interchangeable with the enterprise AOS or Instant products.
Hope that helps.