Sequential consistency
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Sequential consistency is one of the consistency models used in the domain of the parallel programming (e.g in distributed shared memory, distributed transactions etc).
The system provides sequential consistency if every node of the system sees the (write) operations on the same memory part (page, virtual object, cell etc) in the same order, although the order may be different from the "factual" order as defined by time of issuing the operations.
The sequential consistency is weaker than atomic consistency (which would demand that operations are seen in order in which they were actually issued - which is essentially impossible to secure in distributed system, where deciding global time is virtually impossible) and is the easiest consistency model to understand, since system preserving that model is behaving in a way expected by average programmer.
The simplicity is achieved at cost of efficiency: distributed systems with sequential consistency model are, without further optimisation such as speculation, one magnitude slower than those providing weaker models.