ACID is a concept used with Databases. It is an abbreviation. It stands for
- Atomicity - something is either done completely, or not done at all. The state of doing it is not visible outside the database.
- Consistency - The database is in a legal state at all times. When a transaction occurs, it can not break the rules. These rules are about integrity, what is allowed and what is not allowed in certain locations of the database.
- Isolation - There can be more than one transaction occurring at the same time. A certain transaction will not see changes made by other transactions.
- Durability - When a transaction is done, it will be committed. After it is committed, it can no longer be undone.