IFC entities are: "classes of information defined by common attributes and constraints". (ISO 10303-11). They are objects uniquely defined in the IFC model that can be assigned certain attributes and dependencies with other elements of the model. Examples of IFC entities are walls, windows, pillars, etc.
The "IFC Entities" are made up of a geometric part and an information part. The latter, in turn, can be subdivided into properties and relationships between the various elements in the model.