According to the text-book, In the relational database model is a person, place, thing , transaction, or even about which information is stored
More definition at Wikipedia website: http://en.wikipedia.org/wiki/Entity
An entity is something that has a distinct, separate existence, though it need not be a material existence. In particular, abstractions and legal fictions are usually regarded as entities. In general, there is also no presumption that an entity is animate. Entities are used in system developmental models that display communications and internal processing of, say, documents compared to order processing.
Sometimes, the word entity is used in a general sense of a being, whether or not the referent has material existence; e.g., is often referred to as an entity with no corporeal form, such as a language. It is also often used to refer to ghosts and other spirits. Taken further, entity sometimes refers to existence or being itself. For example, the former U.S. diplomat George F. Kennan once said that "the policy of the government of the United States is to seek . . . to preserve Chinese territorial and administrative entity."
The word entitative is the adjective form of the noun entity. Something that is entitative is "considered as pure entity; abstracted from all circumstances", that is, regarded as entity alone, apart from attendant circumstances.