One reason that companies perform exit interviews is to gain insight on the company itself. They want to know what they are doing well and in what areas they can improve in. These interviews are usually conducted through the human resources department.
Termination interviews are conducted when the services of an employee are no longer needed. For example, the employee may be getting laid off or perhaps they were not performing the duties and responsibilities of their job.
A separation interview is conducted when the services of an employee are being transferred.
An exit interview is what takes place between you, your manager, and someone from HR when you are voluntarily leaving your job to take a job at a different company. It usually involves answering questions about your experiences with the company, your reasons for leaving, and what, if anything, could they have done differently to change your mind about leaving your job.
A separation interview is similar to an exit interview in that your leaving your position is usually voluntary except unlike an exit interview you aren't leaving the company. In this situation you are often transferring to the same position in a different department or a different position in a different department. During this interview you usually go over what work you are handing off to whom, and why you are leaving the position.
A termination interview is what takes place between, your manager, and someone from HR when you have involuntarily been terminated from your job be it due to lay offs or being fired. During this interview they give you your termination letter, explain what, if any, your severance package is, and go over the reasons why your position is being terminated.
I have not come across any business practice or management literature that distinguishes exit interview from separation or termination interview. As applicable to human resource management the word 'exit' in 'exit interview' refers to the an employee leaving the employment of a company. The word separation is also sometimes used as synonym for the word exit. an employee may exit or separate a company for various reasons including voluntary retirement, moving to another company or starting own business or engaging in some other work, retrenchment, retirement on superannuation, or termination of services on disciplinary grounds. Thus termination may be considered a particular type of exit or separation.
Companies follow the practice of having an exit or separation interview with the employee to seek his or her feedback about the company. This is done on the assumption that a person who is about to leave the company's employment is not likely to be constrained by fear of incurring displeasure of superiors, in giving free and frank opinion about the company, In this way the company seeks to gain insights on possible causes of dissatisfaction of employees in the company.