Shortcode to get taxonomy term description

code.php

// Using product_brand taxonomy in this example.
add_shortcode( 'product_brand_desc', function() {
	if ( ! is_single() ) {
		return;
	}
	$current_post_terms = wp_get_post_terms( get_the_ID(), 'product_brand', array( 'fields' => 'ids' ) );
	$desc = '';
	if ( ! is_wp_error( $current_post_terms ) && ! empty( $current_post_terms ) ) {
		$current_post_term = $current_post_terms[0];
		$desc = get_term_field( 'description', $current_post_term ); 
	}
	
	return $desc;
} );