Note: This term is specific to CockroachDB, a Distributed SQL database. In other contexts, it may be used differently.
MVCC (Multiversion Concurrency Control) is a protocol that CockroachDB follows to ensure isolation of transactions when concurrent transactions are happening. Without MVCC, if a database is being used in multiple ways at the same time, then someone might see half-written or inconsistent data. MVCC keeps multiple copies of data, so each user sees a snapshot of the database at a particular instant in time, and they won’t see changes until the transaction has been committed.