Source

File: wp-includes/taxonomy.php

function wp_defer_term_counting( $defer = null ) {
	static $_defer = false;

	if ( is_bool( $defer ) ) {
		$_defer = $defer;
		// Flush any deferred counts.
		if ( ! $defer ) {
			wp_update_term_count( null, null, true );
		}
	}

	return $_defer;
}