An app ID is a string used to specify an app, or set of apps. An app ID's primary use is to specify which apps are authorized to be signed and launched.
An app ID has two parts: the team ID followed by the bundle ID search string. The team ID is a 10-character string generated by Apple. Each development team is assigned a unique team ID used to identify all your apps. A bundle ID search string is traditionally a reverse-domain-name style string.
The following guide will show you create an App ID in the iOS provisioning Portal. To create an App ID, you need to have an Apple Developer account and be a member of the iOS Developer Program.