It means your order has arrived at customs for clearing, once cleared it will update to say "now in transit" or something like that, if it doesn't update after a reasonable length of time e.g. a day or so it could have been seized. Occasionally customs have a backlog and shipments takes an inordinate length of time to clear but that is generally the exception and not the rule. It also differs from country to country a fair bit, sometimes the tracking never updates and then the order just arrives, its quite the crap shoot.