But simply put, it keeps the United Kingdom inside an EU customs area indefinitely.
简单来说,这份协议使英国可以无限期地留在欧盟关税同盟。
英语百科
Customs area
A customs area is an area designated for storage of commercial goods that have not yet cleared customs. It is surrounded by a customs border. Most international airports and harbours have designated customs areas, sometimes covering the whole facility and including extensive storage warehouses.