An app group is an Apple platform feature that lets related apps share a common container for files, preferences, and other data. Each app still runs in its own sandbox, but apps signed with the right team identifier and entitlement can read and write the shared area. This is useful for companion apps, extensions, and coordinated features that need to exchange data without using the network.
In cyber security, app groups matter because they change the local trust boundary. If sensitive content is written to a shared container in plaintext, any entitled sibling app can potentially access it, even without a user prompt. Attackers and researchers often look for this kind of misplacement when they assess mobile privacy risks. Defenders should limit shared storage to non-sensitive data, encrypt local files before sharing them, and review which apps and extensions hold the relevant entitlement.