on Jane Friedman site:
Whether you’re writing a novel, memoir or how-to book, a manuscript evaluation can be an economical opportunity to have your work reviewed by a professional editor before you begin querying and submitting. It ideally happens only when you’ve taken your manuscript as far as you can—since it’s not going to do you much good if your feedback consists of comments about revisions you already know you have to make.
A manuscript evaluation is a high-level analysis of your manuscript through multiple lenses:
