Evans: Although REPOSITORIES and FACTORIES do not themselves come from the domain, they have meaningful roles in the domain design. These constructs complete the MODEL-DRIVEN DESIGN by giving us accessible handles on the model objects.
An AGGREGATE is a cluster of associated objects that we treat as a unit for the purpose of data changes. Each AGGREGATE has a root and a boundary. The boundary defines what is inside the AGGREGATE. The root is a single, specific ENTITY contained in the AGGREGATE.