Using deception to obtain confidential information from someone by phone or in person. For example, "social engineers" may persuade someone to reveal an ID or password for a supposed benign purpose ("my computer is down, can I use yours in the meantime"). They can even walk in off the street and pretend to be from IT doing a routine inspection.
Sometimes, a combination of social engineering and hacker skills are used to steal information. However, no matter how secure a network may be, the "con" played by the social engineer is often the most effective way to break in.
The Generic Meaning
Outside the computer world, social engineering means to influence attitudes and behaviors. See phishing
and shoulder surfing