Explain what is meant by dirty read in the context of transactional data processing.

Dirty read is a situation in transactional data processing where one transaction reads data that has been modified by another transaction but not yet committed. If the second transaction rolls back, the first transaction has read uncommitted, and thus unreliable, data.

Example: Transaction A updates a value but has not completed. Transaction B reads this new value. If Transaction A cancels the changes, the data read by Transaction B becomes incorrect.

Dirty reads violate transaction isolation and can lead to errors in business logic. To prevent dirty reads, transaction isolation levels such as "Read Committed" or higher are used.