WordPress get all terms from categories and tags

wp-get-all-terms.php

$term_query = new WP_Term_Query( 
  array(
    'taxonomy' => array('category','post_tag'),
    'order' => 'ASC',
    'orderby' => 'name'
  )
);

if ( ! empty( $term_query->terms ) ) {
  foreach ( $term_query->terms as $term ) {
    echo $term->name;
  }
} else {
  echo 'No terms found.';
}