"a social engineering technique whereby attackers under disguise of a legitimate request attempt to gain access to"
phishing
vishing
backdoor access
shoulder snarfing

It is commonly referred to as phishing.

Explanation:

Phishing is called a social engineering technique because it involves convincing the victim through prolonged email and oral conversations to share his personal information like sensitive passwords and bank details.Some highly skilled and learned yet antisocial groups of people attempt to reach out to working professionals through means like email or telephone and convince them to obey to their instructions for their own benefit.These people who try to gain access to sensitive information of other individuals are often trained negotiators.