What fundamental concept is implied by the transaction isolation level in MySQL?

The transaction isolation level in MySQL determines the degree of visibility of changes made by one transaction to other transactions, as well as controls possible anomalies during concurrent transaction execution.

Main isolation levels:

• READ UNCOMMITTED — transactions can see uncommitted changes of other transactions (dirty read).
• READ COMMITTED — a transaction only sees committed changes, but data can change between queries (non-repeatable read).
• REPEATABLE READ (default level in MySQL InnoDB) — guarantees that data read in a transaction will not change until it ends, preventing non-repeatable reads.
• SERIALIZABLE — the strictest level, transactions are executed sequentially, excluding all anomalies.

Thus, the isolation level controls the balance between performance and data integrity when multiple transactions operate simultaneously.