Delete a branch locally

git branch -d dev

Deletes the branch named dev if its changes are merged with another branch and will not be lost. If the dev branch does contain changes that have not yet been merged that would be lost, git branch -d will fail:

$ git branch -d dev
error: The branch 'dev' is not fully merged.
If you are sure you want to delete it, run 'git branch -D dev'.

Per the warning message, you can force delete the branch (and lose any unmerged changes in that branch) by using the -D flag:

git branch -D dev