dear student

Normalisation is a process which is employed in order to evaluate the performance of the candidates on the basis of similar parametrs for eg. Difficulty level.It basically adjusts the difficulty level across different sessions of the exam.

the competitive exams often take place within different slots. the difficuty level may be easy in one slot and tough in another slot.

so for fair evaluation of marks, marks obtained by candidates across different shifts are normalised. 

hope this helps

All the best!!!