A sockpuppet is a second or subsequent pseudonymous online identity belong to a member of a community. Sockpuppets are used to give the impression of multiple people supporting a viewpoint. Most communities, even those which otherwise allow pseudonymity, do not approve of sockpuppets.

For example, Wikipedia's policy on sock puppetry reads:

The default position on Wikipedia is that editors who register should edit using one account only. The purpose of this policy is to forbid deceptive or misleading use of multiple accounts and to explain where editors may legitimately use a second (alternate) account. A second account used deceptively in violation of this policy is known as a sock puppet.

Further reading Edit