Database model is the relational data representation. In other words, it is the set of all database tables, their fields and relations between tables.
Object model is the set of Delphi classes (see Entity) used for operating model data in the code.
Meta-model is a list of special Delphi classes that describes the database model. It stores description of tables and their data fields, and is used for correct retrieving/storing entities from/to the database.
Entity is a base class intended to represent a database model object in the object model. Entity is specifically designed for use in EntityDAC, its life cycle is completely controlled by a data context and its use is most simple and convenient for the developer.
Mapping is the mechanism that creates the meta-model for the database model and sets the correspondence between entities and meta-model objects.
Data context is a mechanism that manages the entities within their life cycle. Its functions are: creating and initializing new entity instances, retrieving and storing entities from/to the database, storing used entities in the cache for future use, destroying of unused entities.