Your overall page count will change as the physical size of the pages is increased or decreased, and any manual formatting such as hard returns or multiple spaces may not appear as intended. (forums.createspace.com)
These include buttons that make it easy to e-mail or print a page, to adjust the font size of a page, and to navigate the site more easily. (lawsitesblog.com)
The trim size is the physical size of the pages (not the cover if it's a hard cover), measured in inches, horizontal by vertical. (bookdesignmadesimple.com)