A ‘Dual’ is a second account for one user. This means that the user has two separate accounts.
When I created my dual it was not for a nefarious purpose. It was simply that I was on my office computer, didn’t recall a password for a particular account. I wanted to post something topical so created another account and posted.
It was only after I became Me2 that I realised how and why people would create duals.
For example, there are times when you are ‘alone’ on a site. ‘Everyone’ is against you. So your Dual joins you, and you and your Dual can have an exchange which is positive.
When someone attacks You, your Dual can defend you. You and yourself can have a nice friendly chat and bring up many points.
In this way, no one on that site will think you are alone.
Having a ‘Dual’ is a trick many Administrators