Question

Difference between regular reflection or diffuse reflection?

Answer 1

Regular reflection
1) After reflection rays are parallel. 
2) It obeys law of reflection 
3) Surface used for reflection is smooth. 
Irregular Reflection 
1) After the reflection rays are not parallel. 
2) It does not obey law of reflection. 
3) Surface used for reflection is rough.

Answer 2

basically regular reflection reflects light in one direction whereas diffuse reflection reflects in all direction.
regular reflection illuminates a particular patch light falls whereas diffuse reflects all around
regular reflection can't be used to see the item reflecting surface
diffuse reflection can't be used to produce images