Definition:
Spoofing is the practice of deceiving people into believing an email or Web site originates from a source that it does not. The most common type of spoofing is email spoofing, but Web page spoofing and IP spoofing are also very common.
In email spoofing the deception is usually accomplished using software that harvests or generates email addresses from which messages appear to be sent. In Web page spoofing, the hacker will use software to display a Web page they have created to duplicate the actual Web page that's targeted. And in IP spoofing, hackers use software to redirect Web site visitors to false Web pages.