Section refers to a portion of a document in which you set certain page formatting options. It is an important concept in document processing software like Microsoft Word.

Explanation:
When you create a document, it can be divided into sections to apply different formatting options such as margins, orientation, headers, footers, and page numbers. Each section can have its own unique set of formatting settings, allowing you to customize various aspects of your document.

Here's a breakdown of the different elements related to sections in document processing software:

1. Page:
A page refers to a single sheet of paper that contains content. It is the basic unit of a document.

2. Document:
A document refers to the entire file or project you are working on. It can contain multiple pages and sections.

3. Section:
A section is a portion or subdivision of a document. It is a way to divide the document into different parts with distinct formatting options. Each section can have its own set of page formatting settings.

4. Page Setup:
Page Setup is a feature in document processing software that allows you to define and modify the formatting options for a section or the entire document. It includes options such as page size, margins, orientation (portrait or landscape), headers, footers, and page numbering.

When you want to change the page formatting options for a specific portion of your document, you need to create a new section. By inserting section breaks, you can separate different areas of your document and apply specific formatting settings to each section.

For example, if you want to have different header and footer information on the first page of your document or if you want to change the page orientation from portrait to landscape for a specific section, you can do so by modifying the page setup options for that particular section.

In conclusion, the correct answer is Section as it is the portion of a document where you can set certain page formatting options.