Wikipedia:
An atomic commit is an operation where a set of distinct changes is applied as a single operation. If the atomic commit succeeds, it means that all the changes have been applied. If there is a failure before the atomic commit can be completed, such as the Internet line disconnecting or a conflict that cannot be automatically resolved, the "commit" is aborted and all changes that have taken place are reversed (rolled back). In either case, atomic commit leaves the system in a consistent state. The word atom is used in its classical sense: an indivisible unit.