Description (of post term) (tag)

category_description()

Gets the description of the category, which is specified on the category editing page in the admin panel (posts > categories).

get_the_archive_description()

Retrieves the description of the post type, category, tag, term, or author archive page.

tag_description()

Gets the description of the tag, which is set when creating/editing the tag in the admin panel.

term_description()

Gets the description of the term (taxonomy element: tags, categories, etc.) that is specified on the term creation/editing page.

the_archive_description()

Display the description of the post type, category, tag, term, or author archive page.