ANSWER:

This is backbiting.

Only when supervisors talk about an employee to assess him or to train him that this won’t be backbiting and in similar cases. 

Sheikh, In my company there are many employees and usually we talk to each other about the other employees work related performance,usually its negative comments related to work,is this backbiting,Eg:”This manager is very lazy as he didnot submitted document yesterday which caused delay”