An outline of a novel is basically called a Chapter-by-Chapter Outline
In fact it isn't an outline in the A, B, C, 1. 2. 3. a, b, c -- type of outline you learned in school.
A Chapter-by-Chapter Outline -- Novel Outline -- or -- Chapter-by-Chapter Synopsis is actually the following:
A short 1 - 2 paragraph synopsis of each chapter - with the beginning, any key plots, character introductions and the chapter ending spelled out.
Each chapter goes on a separate page, double spaced.
A good example of one is in the book:
Formatting & Submitting your Manuscript -- 2nd edition
by Cynthia Laufenberg and the Editors of Writer's Digest Books
Page #134 with examples on pages 136-137
The reason agents and/or editors ask for this is: they want to see if you can follow through with your plots and they want to see how the story evolves through the chapters.