Define BIM and what are the major advantages and disadvantages of BIM (Revit) to CAD?

Building Information and Modeling is mainly used to provide 3D or 4D representation.

BIM is defined as Building Information Modeling (BIM) is a digital representation of physical and functional characteristics of a facility

Advantage and Disadvantage of BIM over CAD 

CAD usvally deals with plan section and elevation which is 2 dimentional and 3 dimentional (width, height and depth).

where as BIM deals with providing the particular information in 3 dimentional (width, height and depth), 4 dimentional (cost), 5 dimetional (time )