There are different definitions of social engineering. In the Political Science realm, it refers to:
"efforts to influence particular attitudes and social behaviors on a large scale, whether by governments, media, academia or private groups in order to produce desired characteristics in a target population. Social engineering can also be understood philosophically as a deterministic phenomenon where the intentions and goals of the architects of the new social construct are realized. Social engineers use the scientific method to analyze and understand social systems in order to design the appropriate methods to achieve the desired results in the human subjects."(https://en.wikipedia.org/wiki/Social_engineering_(political_science))
In the Information Security realm, it refers to:
"the psychological manipulation of people into performing actions or divulging confidential information. A type of confidence trick for the purpose of information gathering, fraud, or system access, it differs from a traditional "con" in that it is often one of many steps in a more complex fraud scheme. It has also been defined as "any act that influences a person to take an action that may or may not be in their best interests." (https://en.wikipedia.org/wiki/Social_engineering_(security))