In short, "pretexting" means impersonating someone else. Pretexting is the act of creating and using an invented scenario (the pretext) to persuade a targeted victim to release information. While it is typically done over the telephone, data brokers also obtain confidential information using computers.
Pretexting is more than a simple lie, however, as it involves some prior research to establish legitimacy in the mind of the targeted individual (such as knowing a Social Security number in advance of contact). This technique is often used to trick a business into disclosing customer information, and is it used by private investigators to obtain telephone records, utility records, banking records, medical records, places of employment, and other information. Pretexting can also be used to impersonate co-workers, police, bank, tax authorities, or insurance investigators, or any other individual who could have perceived authority in the mind of the targeted victim.
Historical perspective: In 2006, Hewlett-Packard hired private investigators to help find the source of information leaks. They used slimy --but legal-- tactics such as digging through trash, sending fake e-mails loaded with hidden tracking software, and tailing journalists who were communicating with HP employees. They crossed the legal line when they used pretexting, or posing as someone else in order to get phone records. The chairman of HP and half a dozen board members resigned or were fired as a result, and the entire debacle shed new light on the possibilities of employee monitoring in the digital age.