It is one of the simplest methods for prioritisation. This is useful if you have to reach a consensus in a team meeting.
Must: Critical. Without this, product/release is a failure
Should: Important, but not critical for the release
Could: Desirable but not necessary. Example: If it is there, customer satisfaction will increase
Would: Least critical. Can be ignored for this release. Plan it for later
Product managers can use it convince stakeholders in a quick meeting. Especially, when they do not want to know the in-depth details
Label the tasks in hand with “Must”, “Should”, “Could” or “Would”.