Source

File: wp-includes/class-wp-query.php

public function is_tax( $taxonomy = '', $term = '' ) {
		global $wp_taxonomies;

		if ( ! $this->is_tax ) {
			return false;
		}

		if ( empty( $taxonomy ) ) {
			return true;
		}

		$queried_object = $this->get_queried_object();
		$tax_array      = array_intersect( array_keys( $wp_taxonomies ), (array) $taxonomy );
		$term_array     = (array) $term;

		// Check that the taxonomy matches.
		if ( ! ( isset( $queried_object->taxonomy ) && count( $tax_array ) && in_array( $queried_object->taxonomy, $tax_array, true ) ) ) {
			return false;
		}

		// Only a taxonomy provided.
		if ( empty( $term ) ) {
			return true;
		}

		return isset( $queried_object->term_id ) &&
			count(
				array_intersect(
					array( $queried_object->term_id, $queried_object->name, $queried_object->slug ),
					$term_array
				)
			);
	}