Prioritization technique for managing requirements.

Snippet from Wikipedia: MoSCoW method

The Moscow method is a prioritization technique used in management, business analysis, project management, and software development to reach a common understanding with stakeholders on the importance they place on the delivery of each requirement; it is also known as MoSCoW prioritization or MoSCoW analysis.

The term Moscow itself is an acronym derived from the first letter of each of four prioritization categories: M - Must have S - Should have C - Could have W - Won't have

The interstitial Os are added to make the word pronounceable. While the Os are usually in lower-case to indicate that they do not stand for anything, the all-capitals MOSCOW is also used.