git-check-ref-format(1)

A reference is used in Git to specify branches and tags. A branch head is stored in the refs/heads hierarchy, while a tag is stored in the refs/tags hierarchy of the ref namespace (typically in $GIT_DIR/refs/heads and $GIT_DIR/refs/tags directories or, as entries in file $GIT_DIR/packed-refs if refs are packed by git gc). They can include slash / for hierarchical (directory) grouping, but no slash

[ymkjp]

Gitの有効なブランチ名（refの形式）

[dmp939]

git branch -d @{-1} で一つ前にいたブランチを削除でき便利