as written here

http://docs.unity3d.com/Documentation/Components/SL-BuiltinValues.html

float4x4 UNITY_MATRIX_MV

Current model*view matrix

float4x4 _Object2World

Current model matrix

my question seems a basic one in OpenGL but I am new and not sure where to find the difference

an extensive explained reference will be appreciated

Cheers

So:

UNITY_MATRIX_MV Convert the model to the view - as in the Camera is at 0,0,0

UNITY_MATRIX_MVP Convert the model to the projection - including the Camera clip planes, field of view etc

_Object2World Convert the model to the World coordinates - the model vertices are in local coordinates, afterward the position multiplied is in world coordinates

UNITY_MATRIX_IT_MV Inverse of the MV matrix - used to convert normals (directions) to the view