git commit --amend is a command in Git that allows you to modify the most recent commit. It can be used to combine staged changes with the previous commit instead of creating an entirely new commit. It can also be used to simply edit the previous commit message without changing its snapshot. When you amend a commit, it replaces the previous commit entirely, meaning the amended commit will be a new entity with its own reference. To Git, it will look like a brand new commit.

Amending a commit is useful when you need to make small changes to the most recent commit, such as correcting a typo in the commit message or adding a file that was forgotten in the previous commit. However, amended commits are actually entirely new commits, and the previous commit will no longer be on your current branch. This has the same consequences as resetting a public snapshot. Therefore, it is recommended to avoid amending a commit that other developers have based their work on, as it can be a confusing situation for developers to be in and it’s complicated to recover from.

To amend a commit, you can use the git commit --amend command. If there are no changes staged, running this command when there is nothing staged lets you edit the previous commit’s message without altering its snapshot. If there are changes staged, you can add or remove changes from the Git staging area to apply with a --amend commit. In GitHub Desktop, you can amend a commit by right-clicking on the most recent commit and selecting "Amend commit".

It is important to note that amending a commit that has been pushed to the remote repository requires a force push to overwrite the commit history in the remote repository. Overwriting commit history may cause confusion for other collaborators working with the repository, because they may have already based work on the commit you have amended.