A valid version branch name is a permitted branch that users can choose when performing a command that assigns a version to a new item revision. Using the Administration Console, you can define valid version branches, and then make them available to a specific project using the desktop client, the web client, the command-line interface, or the ISPF client. When users add, check out, revise, or edit a revision from that project, they are allowed to choose from the list of available version branches.
In the case of a stream, a single branch name is assigned that is used for all new item revisions in that stream. When you create a new stream, you can either assign an existing branch name or create a new one as a part of the Create Stream process.
The use of version branch names within a project is optional, but a stream must have a branch name.