Hi Kushi,
CL_CRM_BOL_BO_COL is generic class and CL_CRM_BOL_ENTITY_COL is specific class.
Because BOL_CO_COL is super class of BOL_ENTITY_COL.
When we on the top in hierarchy then it is generic (any one can use that according to their requirement) and when we go down then we moves towards Specific.
Take an simple example :
Here Vehicle is generic class because we can use this class for TwoWheeler also and FourVehicle class also can be used for MarutiFourVechicle class.
Regards,
Ankit