Nintendo network login

The sign in window on the Miiverse website asking for a Nintendo Network ID and password

A Nintendo Network ID is the account that one may use to access all functionality of the Nintendo Network, such as Miiverse. One may have up to 12 accounts registered at a time on a Wii U, and one on a 3DS. However, a particular NNID may be banned from Miiverse, but it doesn't affect other services. The login and display name of a Nintendo Network ID must be between 6 and 16 characters.