Definition
A Minimum Marketable Feature (MMF), the smallest set of functionality that must be realized in order for the customer to perceive value.
A feature is something that is perceived, of itself, as value by the user. “Marketable” means that it provides significant value to the customer; value may include revenue generation, cost savings, competitive differentiation, brand-name projection, or enhanced customer loyalty.
Further Reading
BOOK: Agile Product Management with Scrum by Roman Pichler