Hi.From what i understand mulatto means mixed.It is a word that was mainly used to describe how a person physically looked.On census records many enumerators listed mulatto for people who didn't all the way look typically negro or physically black or negro.Sometimes the person listed as a mulatto was a mixed person who really had one white parent and one black parent(the true webster dictionary meaning of this word) or it could be one white parent and one native american parent, or a combinations of ethnic makeups.Sometimes a person was listed as mulatto who may have been a 3rd or 4th generation mixed person.
I also wanted to say that not all mulattoes were or are creoles even if they do come from Louisiana.Also not all mulattoes were free.Many slaves were listed as mulattoes.

Ihoped this helped:)