Someone hired by a company to pose as a customer in order to evaluate the quality of its service.

(now Australia, slang) A sausage. / (Australia, slang) A pie.

A bag whose contents are unknown. / A surprise package randomly picked, a lucky dip. / A non-specific mixed lot of a product at the supplier's choice.

Any river snail of the family Viviparidae.

plural of mystery snail

(Britain) A short-duration outing by coach to a destination that is not revealed in advance

(informal, derogatory) Any processed meat product whose animal source is not readily identifiable.

plural of mystery meat

plural of mystery tour

(marketing, business) An individual hired by a company to pose as a customer in order to evaluate the quality of its service. / (television) A guest star whose identity is kept secret.