Description
A paragraph of text on the options page, to explain the fields that follow.
In the editor

| Setting | What it does |
|---|---|
| Description | The text. Links, bold and other formatting of post content are allowed. |
| Additional CSS Class(es) | Extra CSS classes for the paragraph. |
On the options page

The text is a <p>, filtered like the content of a post (wp_kses_post()).
The value
A description stores nothing.