CodeCop is a very interesting new addition for AL developers. it is a software artifact that checks, like a cop at the corner of the streets, if the code written respects specific rules (coding rules). This concept never existed in the old CSIDE and C/AL developers just keep their own rules in mind without anything specific to check whether these are applied.
You can find a basic reference for AL CodeCops at https://docs.microsoft.com/en-us/dynamics365/business-central/dev-itpro/developer/devenv-using-code-analysis-tool.
There are different type of Codecops, depending on the deployment type. These are used to bust specific unwanted semantic code and make the developer's coding more restricted and less open to fantasy or fancy solution, hard to check and maintain even by smart developers, and, overall, deviating from the standard Microsoft Development...
