Butter Pecan is a type of ice cream. It can be Sugar Free, or not. As the name suggests, there are pecans, in a mixture of butter, and ice cream. It was originally created as an Ice Cream that was butter, and milk only. Apparently, but not yet proven, pecans fell in the mixture, and it was so popular, that is how we got Butter Pecan.
More information on the Wikipedia page [1].
Butter Pecan Ice Cream.