What is the difference between a mandatory and a desirable requirement?

A mandatory requirement is a criterion that must be met for a project or product to be considered acceptable or compliant; failure to meet it can result in disqualification or rejection. In contrast, a desirable requirement is a criterion that is preferred but not essential; meeting it enhances the quality or functionality but is not necessary for approval. Essentially, mandatory requirements are non-negotiable, while desirable requirements are considered additional benefits.