Git reflog is a powerful tool that acts as a chronological logbook for a Git repository, recording all changes made to the HEAD pointer and enabling developers to undo mistakes by navigating through the repository's history. It stores every modification, allowing users to rewind time and recover from errors such as accidental commits, deleted branches, or botched rebases. Stored in the .git directory, reflog can be accessed and filtered using time qualifiers to pinpoint specific moments in a project's history. This capability is crucial for correcting mistakes like a failed rebase by identifying the correct commit to revert to. While reflog is not a substitute for good engineering practices, it can be a lifesaver in worst-case scenarios, providing a way to restore a repository to a desired state when things go awry.