The ACID properties are the desired properties of a database Transaction. They are:
Atomicity - A transaction must takeplace completely or not at all.
Consistency preservation - A transaction must take the database from one consistent state to another. Consistent states in a database are those which satisfy all of the constraints specified. (Frequently involves things like updating foreign keys.)
Isolation - A transaction mustnot make it's changes visible to other transactions until it is committed.
Durability (permanence) - Once a transaction changes the database and the changes are committed, these changes must never be lost from subsequent failure.