CSP is one of the many ways of reasoning about concurrent systems. It emphasizes on the idea of a channel which enables communication between producers and consumers and where the channel itself is fundamentally decouple from either producers or consumers.
The easiest way of thinking about a channel is to think about a queue. A queue is very simple, it is a data structure where one may only push data to the end of a queue and may only read data from the front of the queue.
In pseudo-code: