Command Query Responsibility Segregation
At its heart is the notion that you can use a different model to update information than the model you use to read information. For some situations, this separation can be valuable, but beware that for most systems CQRS adds risky complexity.
A request to change the state of the system. Commands should return no data, but state changes should emit an event.
Requests for data in the domain. May be an entirely different data store than the commands, optimized for reads.