Yes, it is known as an open border. Of course. Just as there must be a border between Spain and Portugal, as otherwise you would not know where one country started and the other ended. However, it is not essential to have controls on a border. For instance, goods frequently arrive by plane, and most airports are a long way from a country's borders. Customs checks have to be done at the airport freight terminals, usually many miles inland from the country's borders. Another example previously quoted here are the customs facilities at Stop 24 on the M20 in Kent, where lorries can be checked by customs before crossing the channel - although actually 15 miles inlamnd from Dover. You have confused the statement that there will be no hard border in Ireland for meaning that there will be no border on the island of Ireland. Nobody is suggesting that there will be no customs checks, They have said that there will be customs checks but that these will not take place on the physical border.