Gaps at the edges of your document where your printer may not be able to print. Publisher can get this information from your printer when you create the document.
Two pages facing one another, usually with an even number on the left and odd on the right.
Dots Per Inch, a measure of the resolution at which something will print. 300dpi is good for photos, but the number you choose depends on the purpose of your document and what it’s printed on.