Sockpuppeting is creating multiple accounts to avoid a ban in any way. It is even worse if a user does not tell his fellow users that he is the sockpuppet. When it is proven without the userp latying a part in it, the ban will be longer. For more info, see the upcoming policies.
Creating multiple accounts is not sockpuppeting. People can make multiple accounts as a backupp for their original account, as long as they tell the other users that it is them and not someone else.
The term sockpuppeting comes from the original wikipedia policies.