A monograph is the word used by the academic publishing community for a book. To be precise, it is a book on a single subject, usually by a single author. This differentiates it from an edited collection, in which a number of different people write chapters of varying quality and deliver these late to a lead author, who will spend much of their time avoiding the calls of their commissioning editor while thinking up ever more extravagant reasons why the deadline for delivery of the completed text should be extended again. The monograph is not that.
For those writers that are new to this area, the language around academic publishing is really the first test. If you think of the scene in Harry Potter where Harry plays chess against living pieces, when losing will mean his fiery death in a dark chamber, you will be in the right ballpark. Getting the language wrong in your proposal will not generally result in your actual death, of course, just professional. It will only be your pride and honour that lies crushed beneath the stony hoof of a CGI enhanced publishing horse. So that’s ok.
For new academics entering the field, and considering submitting their proposals to academic publishers, there are some great talks being run at various times throughout the year. The best advice we could give would be to take good advice.