Container: "an object used for or capable of holding, esp for transport or storage, such as a carton, box, etc." - Dictionary.com. This class describes the object in which the specimen is contained, such as its capacity, etc. Some containers are manufactured such that they contain a pre-defined substance that may act to preserve, maintain or enhance the particular nature or component of the specimen. For example, a "blue top tube" typically contains an anticoagulant such as citrate. It is therefore important to know what kind of container the sample is in, as the condition of the sample may be affected. "An Entity that holds other Entities." - HL7 Version 3. "The container holding the specimen. The recursive nature of containers; i.e. blood in tube in tray in rack is not addressed here." - HL7 FHIR, Specimen.container