Lifting the corporate veil means that ignoring the rule of separate legal entity of the company or disregarding the corporate personality and looking behind the real person who is in the control of company.

It should be noted that lifting is only permissible in exceptional cases. It is noted that when a company is unable to fulfill its statutory requirements the lifting is done and the person who is responsible for such act is held liable. Example in case of reduction in membership below statutory minimum, misdescription of name of the company, fraudulent training and Ultra Vires acts etc.

Sometimes the corporate veil is lifted under judicial decisions also. As company being an artificial person cannot itself act in deceptive and fraudulent way. Hence when it is found that any member or such person by taking advantage of rule of corporate veil acts in such way then he should be personally liable for such act. So the lifting is done for the purpose like. Example protection of revenue, prevention of fraud or improper conduct, determining the character of the company and check avoidance of welfare legislation etc.
Hope clear.