WordPress at a glance
function is not described

is_subdomain_install() WP 3.0.0

Whether a subdomain configuration is enabled.

No Hooks.

Return

true|false. True if subdomain configuration is enabled, false otherwise.

Usage

is_subdomain_install();

Changelog

Since 3.0.0 Introduced.

Code of is_subdomain_install() WP 5.7

<?php
function is_subdomain_install() {
	if ( defined( 'SUBDOMAIN_INSTALL' ) ) {
		return SUBDOMAIN_INSTALL;
	}

	return ( defined( 'VHOST' ) && 'yes' === VHOST );
}