There are some exceptional states that branches can be in. You should rarely encounter them - but in case you do you can read up on them, here.
Normally the HEAD pointer in Git stores the name of the branch you are currently working on. However, the "checkout" command is flexible enough to not only check out branches: when you check out anything other than a local branch name (for example a tag, a remote branch, or a commit's SHA1-ID that is not the tip of any particular branch) you are left with an anonymous branch - called a "detached HEAD".
You can commit in this situation but must keep in mind that no named branch will get updated hereby. This can lead to losing the commit as soon as you check out something else because it might not be referenced by anything.
Create or check out a branch to get back to a "normal" working situation.
NOTE:A detached HEAD can be part of a rebase operation: If a merge conflict occurs during the rebase, a special "(no branch) HEAD" item will appear in the Sidebar. After solving all rebase conflicts, the temporary item will disappear again.
Normally, branches in Git share a common commit at some point in history. An orphaned branch is an exception: it's an empty branch starting with absolutely no commits.
The first commit on this branch will therefore have no parent commit and will be the start of a new history that is totally disconnected from all other branches and commits in this repository.