Source

File: wp-admin/includes/class-wp-terms-list-table.php

public function column_description( $tag ) {
		if ( $tag->description ) {
			return $tag->description;
		} else {
			return '<span aria-hidden="true">&#8212;</span><span class="screen-reader-text">' . __( 'No description' ) . '</span>';
		}
	}