Baiting is a social engineering technique that relies on the curiosity of people.
The attacker leaves an infected medium, such as a USB flash drive, in a location where it can easily be found, e.g. a bathroom, an elevator, the sidewalk, etc. The attacker then waits for the victim to pick up and use the device.
When the victim inserts the device into a computer to view its contents, (s)he unknowingly installs malware that gives the attacker unfettered access to the victim's PC, unless the computer's antivirus software blocks it.