About pull request merges→
You can merge pull requests by retaining all the commits in a feature branch, squashing all commits into a single commit, or by rebasing individual commits from the head branch onto the base branch.
Merging a pull request→
Merge a pull request into the upstream branch when work is completed. Anyone with push access to the repository can complete the merge.
Closing a pull request→
You may choose to close a pull request without merging it into the upstream branch. This can be handy if the changes proposed in the branch are no longer needed, or if another solution has been proposed in another branch.
Reverting a pull request→
You can revert a pull request after it's been merged to the upstream branch.