CQS: It is a programming principle that says you should separate operations that change data (commands) from those that read data (queries). If you have a method, for instance, it should either return something or update something, but not both.

CQRS: By dividing the design of the entire system into two sections, one for managing commands (writing or modifying data) and another for managing queries (reading data), CQRS expands on this idea. Each side can have its own database or model to optimize how they work.

So, CQS is the basic rule, and CQRS is like an advanced version of it used for bigger systems where you want to handle reading and writing differently.