MVCC
Acronym for "multiversion concurrency control". This technique allows InnoDB transactions with certain isolation levels perform consistent read operations; that is, to query rows that are being updated by other transactions, and see the values from before those updates occurred. This is a powerful technique to increase concurrency, by allowing queries to proceed without waiting due to locks held by the other transactions.
This technique is not universal in the database world. Some other database products, and some other storage engines within MySQL, do not support it.
See also ACID.
See also concurrency.
See also consistent read.
See also isolation level.
See also lock.
See also transaction.