The general connotation of the word 'entity' is often of a being/creature/organism/lifeform with some kind of intelligence but not necessarily a concrete material existence. eg. God is often referred to as an 'Entity' with no corporeal[?] form.
However, the word 'entity' does not necessarily imply that the thing in question is intelligent, or living, and can be used of inanimate objects or non-material concepts. In this sense, the word is often just used as a synonym for "thing".
wikipedia.org dumped 2003-03-17 with terodump