Outline Levels

link to Outlining

An outline level format is formatting that you can use to assign a hierarchical level to paragraphs in your document.
This formatting is not visible
Applying level 1 outline-level formatting to a paragraph does not change the visible formatting
Every paragraph in your document has an outline-level format associated with it.
Body Text - no outline
Heading 1 - Level 1
The built-in heading styles have corresponding outline-level formatting assigned to them

Outlining toolbar
Lets you apply outline levels quickly (even in views other than Outline)
Lets you update the table of contents
Update TOC button and the Goto TOC button work only with the first TOC in your document and only with TOCs created from built-in styles in Word.

If you use Outline levels to mark the headings you can select the Outline level option.
Each outline level is automatically assigned a corresponding TOC level