Atomic Operation.

Definition

A data operation that executes as all-or-nothing — either every change it contains is applied, or none is, with no intermediate state ever visible. This protects data integrity when several processes write at the same time, because no reader can observe a half-applied update. In practice it means using the database's own atomic primitives (single-document updates, transactions, conditional writes) instead of read-modify-write sequences that can interleave.