What is called regular and irregular reflection of light?

Regular reflection: when a parallel beam of light is incident on a plane or smooth surface, a beam remains parallel after reflection in a specific direction. Such reflection is called regular reflection. The figure below illustrates regular reflection.

Example: Reflection of light by plane mirror.

Irregular reflection: when a parallel beam of light is incident on rough or irregular surface like Book, stone etc., the beam does not remains parallel but spreads over wide region after reflection. Such reflection is called irregular reflection. The figure below illustrates irregular reflection.

Example: we can see book, table, and chair etc. due to irregular Reflection of light these objects.