What is this type of word called: Mr., Ms., Dr.? In the document I am using, it is referred to as the "prefix", but I don't think that is correct.
"Title" and "honorific" both describe that type of word.
Title or in some cases courtesy title.
I prefer to call those 'appellations.' To me, 'honorific' connotes that it's associated with a position. 'Title' seems neutral enough but it also seems like it's more superfluous, not integral to the naming of something.
AP Stylebook calls it a courtesy title.
That would be called a "style."
Edit: It can also be a mode of address, if used in that way.