ACID Properties are the key properties of transaction processing within a database. A transaction is usually a collection of one or more statements.
Atomicity - Transactions either occur (all queries commit) or don't (rolled back executed queries reversed).
Consistency - All constraints of the database must be satisfied before and after a transaction.
Isolation - The transaction should be carried out without any other process being able to see the intermediate state.
Durability - After a transaction has committed, it's effects should persist, even in the event of a database failure.
http://en.wikipedia.org/wiki/ACID
