Filters the duplicate term check that takes place during term creation.

Term parent + taxonomy + slug combinations are meant to be unique, and wp_insert_term()
performs a last-minute confirmation of this uniqueness before allowing a new term
to be created. Plugins with different uniqueness requirements may use this filter
to bypass or modify the duplicate-term check.

$duplicate_term = apply_filters( 'wp_insert_term_duplicate_term_check', $duplicate_term, $term, $taxonomy, $args, $tt_id );