An .ipa is the iOS equivalent of an installable app
An IPA (iOS App Store Package) is a zip archive containing the compiled app binary, resources, and a signed bundle. It is the file you upload to App Store Connect when you submit to the App Store, and the file TestFlight and enterprise distribution use as well.
Unlike Android's .aab, an .ipa is installable: sideload it onto a device and it runs. That is why the iOS world talks about 'sideloading': installing an ipa directly, without the App Store.
The signing catch (the part nobody mentions first)
Every ipa is signed with a distribution certificate and a provisioning profile that binds the app to a specific bundle identifier and your Apple Developer team. Without valid signing, the ipa does not install on anything. This is deliberate: Apple's signing is the mechanism that keeps iOS locked down, and it is exactly why 'just give me the ipa' is never the whole story.
A provisioning profile is tied to the app's bundle id. That matters if you plan to update an app later: if each build gets a fresh random bundle id, your profile stops matching and the update fails. Tools that build for you need to keep the identifier stable when signing. Tapbound does this for signed builds on purpose.
What you can do with your ipa
Upload it to App Store Connect for review, distribute it to testers through TestFlight, or install it on devices you control for testing. What you cannot do is distribute it freely to the public outside the store without enterprise certificates, which are reserved for companies distributing to their own employees.
The practical rule: your ipa is your app archive, your signing is your responsibility, and the App Store review is the gate you walk through yourself.
How Tapbound handles iOS
Tapbound builds the ipa, but the signing credentials are yours: you provide your distribution certificate, provisioning profile, and (for push) your APNs key in the dashboard, and the build uses them. If you want an ipa, valid Apple credentials are a requirement, not an option, by design, because the alternative is someone else holding your Apple identity.