Wikipedia:Sock puppetry
From the Simple English Wikipedia, the free encyclopedia that anyone can change
A sock puppet is an extra username used by a Wikipedian who already has one or more accounts. The Wikipedian who uses a sock puppet may be called a sock puppeteer. Using sock puppets is usually discouraged. Some people use sock puppets to violate Wikipedia rules or cause disruption. Using multiple accounts is not always bad. When people use sock puppets, it is recommended that they link to their original account. It will be easier to know the status of an account.
Some people feel a Wikipedian should not have more than one account. Some others feel if sock puppet accounts are used for good purposes, then it is fine (e.g one creates a sockpuppet to edit on public computers). See this page for information on how sock puppetry affects other online communities.