他在页边空白处做笔记。

He made some notes in the margin.

本页空白

Это пустая страница

[十几页空白]

[полтора десятка пустых листов]

书中的衬页(空白页, 以备注释用)

прокладной лист в книге; прокладные листы в книге

横格练习簿的页间已插入空白页。

The exercise book has plain pages interleaved between its lined ones/has lined pages interleaved with plain ones.

行首空格白边与缩进行行首之间的空白处

The blank space between a margin and the beginning of an indented line.