A quick search on Google returns a definition of Social Engineering as;
(in the context of information security) the use of deception to manipulate individuals into divulging confidential or personal information that may be used for fraudulent purposes.
"people with an online account should watch for phishing attacks and other forms of social engineering"
It is a type of hacking that doesn't rely on coding or manipulation of computers, but rather - it's the manipulation of people!
Phishing is defined by google as; the fraudulent practice of sending emails or other messages purporting to be from reputable companies in order to induce individuals to reveal personal information, such as passwords and credit card numbers. It is relatively common.
Vishing (as shown in the video below) is where the information is gathered using voice, where the visher is manipulating the other party into providing information. It's interesting that vishers have to have a good level of skill & be able to quickly think on their feet in order to get the job done effectively. Some of them are even known to do standup comedy open mic nights in order to fine tune their ability to think fast and keep calm.
This post will hopefully bring more awareness to the fact that these types of hacks are a real thing that you should act accordingly, and think carefully about who is actually calling you & what information you provide.