What does CQRS stand for and what is the core idea behind it?

CQRS stands for Command Query Responsibility Segregation. Its core idea is to separate the part of a system that handles commands — requests to change something — from the part that handles queries — requests to read something — and let each one be modeled and optimized entirely independently, rather than forcing one shared model to serve both jobs. The command side is optimized for correctness: validating business rules and deciding whether a change is allowed before applying it. The query side is optimized for speed and flexibility: answering questions fast, shaped exactly like whatever screen or report is asking. The name sounds intimidating, but the underlying idea is simply that writing and reading are different jobs, and each deserves a model built for what it actually needs to do.