An false online identity used for the purposes of deception, like lonelygirl15, it is typically created by a person or group in order to promote their own opinions or views.

It's a reference to the manipulation of a simple hand puppet made from a sock and originally referred to a false identity assumed by a member of an Internet community who spoke to, or about, himself while pretending to be another person.

The term morphed to include other misleading uses of online identities, such as those created to praise, defend or support a third party or organization, or to circumvent a suspension or ban from a website. A significant difference between the use of a pseudonym and the creation of a sockpuppet is that the sockpuppet poses as an independent third-party unaffiliated with the puppeteer. Many online communities have a policy of blocking sockpuppets.

NetLingo Classification: Online Jargon