I call it a Preface, and it's only 1 page, but it probably carries the same stigma as a Prologue.
My problem is that I have several POVs and the novel could start with any of them because nothing's given away about the others in the first chapter, they don't start interconnecting until the 3rd and 4th chapters, and some of them don't meet until the end, kind of like The Bridge of San Louis Rey.
So I have three different versions of the Preface depending on what POV I start the novel with.
How do I decide which is the best chapter to start with for an agent the next time one asks for a full?
The one that's in the ever popular 3rd person close with all the pretty prose, the 3rd person omni that starts with action and ends with a cliff-hanger, or the 1st person with a unique voice and the best Question-That-Needs-To-Be-Answered?
I've only been asked for 1 full - it was from a top 5 fantasy/ sci fi agent but then the first reader who requested it took an indefinite leave due to illness and it's been in their que for 9 months since then...but I hope my queries are getting better.
...and that my MS didn't cause his sudden illness!